Abortion-breast cancer hypothesis
Encyclopedia
The abortion–breast cancer hypothesis posits that induced abortion
increases the risk of developing breast cancer
. In early pregnancy
, levels of estrogen
increase, leading to breast
growth in preparation for lactation
. The hypothesis proposes that if this process is interrupted by an abortion—before full maturity in the third trimester
—then more relatively vulnerable immature cells could be left than there were prior to the pregnancy, resulting in a greater potential risk of breast cancer over time. This mechanism was first proposed and explored in rat
studies conducted in the 1980s.
The abortion–breast cancer hypothesis has been the subject of extensive scientific inquiry, and the scientific community
has concluded that abortion does not cause breast cancer. This consensus
is supported by major medical bodies, including the World Health Organization
, the U.S. National Cancer Institute
, the American Cancer Society
, the American College of Obstetricians and Gynecologists, and the Royal College of Obstetricians and Gynaecologists
.
Pro-life
activists have continued to advance a causal abortion–breast cancer link, and in the United States
they have sought legal action to present abortion as a cause of breast cancer when counseling women seeking abortion. This political intervention culminated when the George W. Bush Administration
altered the National Cancer Institute
website to suggest that abortion might cause breast cancer. In response to public concern over this intervention, the NCI convened a 2003 workshop bringing together over 100 experts on the issue. This workshop concluded that while some studies reported a statistical correlation between breast cancer and abortion, the strongest scientific evidence from large prospective
cohort studies
demonstrates that abortion is not associated with an increase in breast cancer risk, and the positive findings were considered to be due to response bias
.
The ongoing promotion of a link between abortion and breast cancer is seen by others as part of the pro-life "woman-centered" strategy against abortion. Pro-life groups maintain they are providing legally necessary informed consent
, a concern shared by some politically conservative politicians. The abortion–breast cancer issue remains the subject of political controversy.
, American College of Obstetricians and Gynecologists, World Health Organization
and the United States National Cancer Institute
have analyzed larger studies regarding induced abortion and breast cancer. Their uniform conclusion is that there is no causative link between induced abortion and breast cancer.
The American Cancer Society
noted with concern that: "The issue of abortion generates passionate viewpoints in many people. Breast cancer is the most common cancer, and is the second leading cancer killer in women (lung cancer is the first). Still, the public is not well-served by false alarms. At this time, the scientific evidence does not support the notion that abortion of any kind raises the risk of breast cancer."
is a professor of biology and endocrinology
at Baruch College
and is the primary advocate of an abortion-breast cancer (ABC) link. While Brind is pro-life and his goal to prove an ABC link, he has published papers in respected journals on other human hormone topics. He has fought against the legalization of RU-486 testifying at a federal hearing that "thousands upon thousands" of women would develop breast cancer as a result of using the drug.
In 1996, Brind published a meta-analysis in the Journal of Epidemiology and Community Health (JECH) which was immediately criticized in a Journal of the National Cancer Institute editorial for concluding response bias was unlikely to have affected their results, "dismissal of the study's limitations, and their blurring of association with causation." The amount of attention the study received prompted a cautionary editorial by a JECH editor. After Brind's study failed to convince the scientific community of a causal relationship, Brind co-founded the Breast Cancer Prevention Institute (BCPI) in 1999 with Angela Lanfranchi, a surgeon and pro-life advocate. In 2003, Brind was invited to the NCI workshop, where he was the only one to formally dissent.
Karen Malec, a former teacher and pro-life activist, started the Coalition on Abortion-Breast (CAB) in 1999 with help from Concerned Women for America
, a conservative Christian U.S. political action group which lobbies for legislation recognizing an abortion-breast cancer link.
While research has shown the protective benefits of full-term pregnancy and lactation in reducing the risk of breast cancer, these benefits are only fully realized in the third trimester when differentiation of new breast growth takes place. The abortion-breast cancer hypothesis posits that if a pregnancy is aborted prior to differentiation it could have an adverse effect by creating and leaving behind more immature cells to be exposed to carcinogens and hormones over time.
Breast tissue contains many lobe
s (segments) and these contain lobules which are groups of breast cells. There are four types of lobules:
During early pregnancy, type 1 lobules quickly become type 2 lobules because of changes in estrogen and progesterone levels. Maturing into type 3 and then reaching full differentiation
as type 4 lobules requires an increase of human placental lactogen
(hPL) which occurs in the last few months of pregnancy. According to the abortion-breast cancer hypothesis, if an abortion were to interrupt this sequence then it could leave a higher ratio of type 2 lobules than existed prior to the pregnancy. Russo and Russo have shown that mature breast cells have more time for DNA repair
with longer cell cycle
s which would account for the reduced risk of parturition against the baseline risk for women who have never conceived and those who have conceived and terminated their pregnancies.
Later on, Russo et al. found that placental human chorionic gonadotropin
(hCG) induces the synthesis of inhibin by the mammary epithelium. Bernstein et al. independently observed
a reduced breast cancer risk when women were injected with hCG for weight loss or infertility treatment
. Contrary to the ABC hypothesis, Michaels et al. hypothesize since hCG plays a role in cellular differentiation and may activate apoptosis
, as levels of hCG increase early on in human pregnancy, "an incomplete pregnancy of short duration might impart the benefits of a full-term pregnancy and thus reduce the risk of breast cancer."
. The researchers were cautious about drawing any conclusions from their unreliable methodologies. During the 1960s several studies by Brian MacMahon
et al. in Europe and Asia touched on a correlation between abortion and breast cancer. Their 1973 paper published in the Journal of the National Cancer Institute inaccurately concluded that "where a relationship was observed, abortion was associated with increased, not decreased, risk." Research relevant to the current ABC discussion focuses on more recent large cohort studies
, a few meta-analyses
, many case-control
studies and several early experiments with rats
.
in Philadelphia conducted a study in 1980 which examined the proposed correlation between abortion and breast cancer. While analysing the effects of the carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) on the DNA labeling index (DNA-LI) in terminal end buds (TEBs), terminal ducts (TDs) and alveolar buds (ABs) of Sprague-Dawley rats in various stages of reproductive development, they found that rats who had interrupted pregnancies had no noticeable increase in risk for cancer. However, they did find that pregnancy and lactation provided a protective measure against various forms of benign lesions, like hyperplastic alveolar nodules and cysts. While results did suggest that rats who had interrupted pregnancies might be subject to "similar or even higher incidence of benign lesions" than virgin rats, there was no evidence to suggest that abortion would result in a higher incidence of carcinogenesis. A more thorough examination of the phenomenon was conducted in 1982, which confirmed the results. A later study in 1987 further explained their previous findings. After differentiation of the mammary gland
resulting from a full-term pregnancy of the rat, the rate of cell division decreases and the cell cycle length increases, allowing more time for DNA
repair
.
Despite the fact that the Russos' studies found similar risk rates between virgin and pregnancy interrupted rats, their research would be used to support the contention that abortion created a greater risk of breast cancer for the next twenty years. In a Discover article sidebar entitled Humans Are Not Rats, Gil Mor, the director of reproductive immunology at the Yale University School of Medicine
, disagrees with Brind on the importance of the rat studies findings. Mor emphasizes that rat studies are ideal for understanding basic processes but because rats have neither breasts nor breast cancer, people like Brind are on "wobbly" terrain.
are calculated as a relative risk
, where 1.0 is no risk; results above, like 1.21, is a 21% increased risk and results below, such as 0.8 is a 20% decreased risk. Relative risks are not necessarily significant. To help assess this a relative risk is followed by a confidence interval
in brackets that shows the likelihood (with 95% confidence) that the relative risk is of significance. Any relative risk with a confidence interval that does not include a value of 1 could be considered significant. For example, the confidence intervals (0.3 – 0.9) and (1.5 – 7.8) are statistically significant, whereas the confidence intervals (0.89 – 7.34) or (0.5 – 1.1) are not. With more data the confidence interval becomes smaller; making it an indicator of the result's statistical reliability.
When a relative risk result actually becomes significant is a difficult and contentious issue. As a small result of 1.41 (1.1 – 1.6) even a significant confidence interval (outside 1.0) may be inaccurate because of response bias
, incomplete data, missed confounding factors, imprecise controls or statistical analysis. If these possible flaws are accounted for they could change the result and/or the confidence interval impacting its statistical significance.
The number of (X/Y ABC cases/controls) gives X as women in the study who have had abortion(s) (induced and/or spontaneous) with breast cancer and Y is women with breast cancer and no abortion history. This dataset is used when calculating the relative risk and provides a way to compare the size of one study to another.
s for breast cancer. Genetics
is a major factor that affects not only a woman's initial breast cancer risk but also her hormonal sensitivity, which in turn affects her susceptibility to a long list of socioeconomic and environmental factors. As Western society
has modernized, environmental
carcinogens, delayed child rearing, less breastfeeding
, hormone replacement therapy
(HRT), hormonal contraception
, early menarche
and obesity
have increased.
If unaccounted for these factors could obscure any individual variable. Scientific studies remove them using case-control
methodology – a woman who has had an abortion (case) is matched with a very similar woman with no abortion history (control) – if this was not done a study could get a false positive or negative
result because of another factor. Examining the ABC issue is all the more difficult because the number of women with an induced abortion history has increased along with other factors in recent decades. Premature birth
adds further complications since uncorroborated studies have indicated it is associated with a history of induced abortion and higher breast cancer risk. One of the most significant controllable factors for breast cancer is parity, or the number of children a women has given birth to. With each full-term pregnancy (particularly the first) the breasts undergo growth and differentiation (in the third trimester); consequently, having no children can increase breast cancer risk.
All of these confounding factors have an effect, directly or indirectly, on hormones which impact breast cancer risk, but they do not significantly affect the results of ABC studies that are properly conducted and take these factors into account with case-control
matching. Hormones being a key factor for cancer risk is well established. Steroidal estrogen
was added to the U.S. federal carcinogen
list in December 2002. The American Cancer Society
(ACS) and the National Cancer Institute
(NCI) note reproductive hormones can elevate breast cancer risk. In particular a Women's Health Initiative
hormone replacement therapy study was cut short from an elevated breast cancer and heart
risk using estrogen with progestin
.
The controversial nature of abortion
may introduce response bias
into interview studies, especially for studies done in decades past when abortion was less accepted; however, the statistical significance of bias has yet to be confirmed. In the late 20th century there was some concern of an increase of breast cancer incidence
. This was found to be partly due to longer lifespans, and the development of better detection methods capable of finding breast cancer earlier.
State Department of Health examined young women with breast cancer in upstate New York (100/63 ABC cases/controls). The results indicated an increased 1.9 (1.2 – 3.0) relative risk for induced abortion and 1.5 (0.7 – 3.7) for spontaneous abortion. Although the study had 1451 breast cancer cases the number of individuals with an abortion history was low; consequently the confidence interval is quite large.
The authors believed that the study was inconclusive as fertility patterns were changing dramatically as a result of legal abortion and increased use of contraceptives. Further they did not have a complete reproductive history of younger women who may still have children affecting the results going forward, but Howe et al. concluded it raised new questions for continuing research as women's recorded contraceptive histories grew. Newcomb and Michels point out it examined only very young women and did not account for some confounding factors such as family history of breast cancer.
The study was funded by Family Health International
, a pro-choice NGO
and although the study started with 49,000 women there were fewer than 5,000 still in the study after 11 years. Lindefors-Harris made no adjustments for family history of breast cancer and the pill, and provides no explanation for a lack of a control group or why the study was limited to women with an abortion before 30 years of age. Brind contends correcting for either of these removes the 23% "protective" effect; and that the study did not account for the difference of nulliparous women in the cohort 41% in comparison to 49% in the general population. Possibly making the protective result about parity (childbearing) rather than abortion.
, which had 1.5 million Danish
women in the study's database (1,338 ABC cases, no controls used). Of those women, 280,965 of them had induced abortions recorded in the computerized registry, which was started in 1973 when having an induced abortion through 12 weeks was legal in Denmark. Although there was an observed increased ABC risk with "increasing gestational age of the fetus at the time of the most recent induced abortion"; the overall relative risk after statistical adjustment came to 1.00 (0.94 – 1.06), meaning zero breast cancer risk. This led to the conclusion that "induced abortions have no overall effect on the risk of breast cancer." The Melbye study's conclusions have been used by many organizations, such as NCI, ACOG, ACS, RCOG and Planned Parenthood
, as key scientific evidence of no ABC link.
Brind and Chinchilli had concerns about the Melbye study database as women in the study were born from 1935 to 1978, but the computerized registry of induced abortions only started in 1973. Melbye et al. responded that if the misclassified older women had their risk underestimated, it would be expected that the younger groups would have a higher risk. The statistically adjusted data indicated this was not the case.
However, the statistical adjustments made were another concern of Brind who argues that the Melbye study accidentally adjusted out induced abortion from the overall results. Instead of case-control matching, Melbye el al. decided to manually remove the many confounding factors that increased over time (e.g. smoking, late child bearing, etc.) and were raising breast cancer risk for younger women relative to older women (birth-cohorts). Brind believes finding exactly zero ABC risk was a consequence and red flag indicating ABC risk was removed along with the confounding factors. Melbye et al. found the point to be self-contradictory, considering Brind wanted birth-cohort matching, then argued against "taking birth-cohort differences into account." Brind has stated that he is against the use of just statistical adjustment and that standard case-control
matching may more accurately account for birth-cohort differences.
Another letter to the editor from Senghas and Dolan questioned why a statistically significant result for induced abortions done after 18 weeks gestation was not specifically addressed in the results section of the Melbye study abstract. Melbye et al. explained even though they found the result "interesting and in line with the hypothesis of Russo and Russo, the small number of cases of cancer in women in this category of gestational age prompted us not to overstate the finding." The first section of Table 1 in the Melbye study:
* The relative risks were calculated separately for each of the five variables, with adjustment for women's age, calendar period, parity, and age at delivery of a first child. CI denotes confidence interval.
† Values were adjusted for women's age, calendar period, parity, age at delivery of a first child, and the other variables shown in the table.
‡ The women with this characteristic served as the reference group.
Other sections listed age at induced abortion, number of induced abortions, time since induced abortion, and time of induced abortion and live-birth history. There was an indication of a relative risk of 1.29 (0.80–2.08) for 12–19 year olds (relative to 20–24 subcohort), and a protective effect 0.74 (0.41–1.33) for women with an induced abortion before and after their first live birth (relative to induced abortion after 1st live birth subcohort); both results were statistically insignificant.
containing 105,716 women (233/1,225 ABC cases/controls) concluded with a relative risk of 1.01 (0.88 – 1.17) "after adjustment for established breast cancer risk factors." Some of the results lead the authors to stipulate: "Although our data are not compatible with any substantial overall relation between induced abortion and breast cancer, we cannot exclude a modest association in subgroups defined by known breast cancer risk factors, timing of abortion, or parity." This modest association was mostly not statistically significant.
have also found little evidence of a link between induced abortion and breast cancer. A study of 267,361 European women (746/2,908 ABC cases/controls), published in 2006, found no significant ABC risk. Another 2006 study involving 267,400 women (872/771 ABC cases/controls) in Shanghai
found no evidence of an ABC link. The Shanghai study also noted that women who had an abortion were at a significantly decreased risk of uterine cancer.
as a collaborative reanalysis on Breast cancer and abortion. This meta-analysis of 53 epidemiologic studies of 83,000 women with breast cancer undertaken in 16 countries did not find evidence of a relationship between induced abortion and breast cancer, with a relative risk of 0.93 (0.89 – 0.96). Organizations and media outlets referenced the Beral study as the most comprehensive overview of the ABC evidence.
Brind maintains that like meta-analysis this study is subject to selection bias
, which he believes is reflected in the removal of 15 published, peer-reviewed studies with positive ABC results for "unscientific reasons"; and including 28 unpublished studies that outnumber the remaining 24 peer reviewed studies. Beral refers to the Lindefors-Harris response bias study as an explanation for higher ABC risk found in interview based studies, however Brind notes in 1998 that Lindefors-Harris conceded their initial conclusion may have been unsound.
by using studies with widely varying results, using different types of studies, not working with the raw data from several studies, and including studies that have possible methodological weaknesses.
The strong reaction to the study particularly in Britain and the United States prompted the editor-in-chief Stuart Donnan to write an editorial. In it he notes:
The Royal College of Obstetricians and Gynaecologists
(RCOG) in March 2000 published evidence-based guidelines on women requesting induced abortion. The review of the available evidence at the time was "inconclusive" regarding the ABC link. They also noted "Brind's paper had no methodological shortcomings and could not be disregarded." However, in 2003 the RCOG concluded that there was no link between abortion and breast cancer. Some of the ABC studies RCOG reference as evidence (pg. 77) have been heavily criticized by Brind in 2005.
headed two studies on the ABC issue looking at women in Washington state. The 1994 study (845/961 ABC cases/controls) results indicated an associated relative risk of 1.5 (1.2 – 1.9) among women who had given birth before having an abortion. This was reflected in higher risks for women younger than 18 or older than 30 years of age who have had abortions after 8 weeks' gestation. Their conclusion emphasized that although the evidence suggested the possibility of a correlative relationship, their findings were not consistent enough to establish one.
The second larger study Daling conducted in 1996 (1,302/1,180 ABC cases/controls) found that abortion was associated with a relative risk value of 1.2 (1.0 – 1.5). The study also found a significant relative risk of 2.0 (1.2 – 3.3) for nulliparous women with an induced abortion at less than 8 weeks gestation. Daling et al. concluded that:
Daling et al. examined the possibility of response bias by comparing results from two recent studies on invasive cervical cancer and ovarian cancer. The results argued against significant response bias. However, Rookus (1996) study noted that patients with cervical cancer may report differently than breast cancer patients.
, China
by Sanderson et al. from the University of South Carolina
and South Carolina Cancer Center at Columbia
concluded that there was no ABC link and that multiple abortions did not put one at greater risk. Since induced abortion is common, legal, and even mandated by the government in China, the recall bias was minimized. Brind has argued that the same factors that make the Chinese study ideal for reducing recall bias also makes them inappropriate for comparison to the West. Specifically, with China’s strict population control, the vast majority of the abortions in the Chinese study were done after the first full-term pregnancy. This differs from North America
.
The Istanbul University
Medical Faculty published a study in 2009 (742/930 ABC cases/controls) of outpatients from clinics, authored by Ozmen et al. it found a 1.31 (1.13 – 1.53) increased ABC risk. The authors point out various potential biases such as selection
, information
and even hospital admission bias may have impacted their results. They believe the large pool of patients available to them and the resulting large size of the study "provided reasonably stable risk estimates."
occurs when women intentionally "underreport" their abortion history, meaning that they deny having an abortion or claim to have fewer abortions than they actually had. This can happen because of the personal and controversial nature of abortion, which may cause women to not want to provide full disclosure. Women in control groups are less likely to have serious illnesses, and hence have less motivation to be truthful than those trying to diagnose their problem. When this occurs, it artificially creates an ABC link where none exists. Three major studies have been published examining abortion response bias.
An editorial by Weed and Kramer focused on how Brind's meta-analysis dismissed bias as a factor. The editorial cites the Lindefors-Harris response bias study that used a "registry-based gold standard to show that healthy women consistently and widely underreport their history of abortion." Weed and Kramer considered this compelling evidence there could be systematic bias within the studies included in the meta-analysis. However, subsequently the Lindefors-Harris conclusion was quietly retracted in 1998. Weed and Kramer believed a causal conclusion was a "leap beyond the bounds of inference" and concluded:
A review of ABC studies was conducted by Bartholomew in 1998. It concluded that if studies least susceptible to response bias are considered, they suggest there is no association between abortion and breast cancer. Chris Kahlenborn, M.D., a pro-life researcher and specialist in internal medicine, observes in his book Breast Cancer: Its Link to Abortion and the Birth Control Pill that if report bias were a significant factor in interview-based studies, then:
The Lindefors-Harris (1991) study (317/512 ABC cases/controls) was the first major study to examine response and recall bias. It used the data of two independent Swedish
induced abortion studies, and concluded there was a 1.5 (1.1 – 2.1) margin of error due to recall bias. However, eight women (seven cases, one control) included in this error margin apparently "overreported" their abortions, meaning the women reported having an abortion that was not reflected in the records. It was decided that for the purposes of the study, these women did not have abortions.
The 1994 Daling study examined the findings on overreporting of the Lindefors-Harris study and found it "reasonable to assume that virtually no women who truly did not have an abortion would claim to have had one." In 1998 the co-authors of the Lindefors-Harris study acknowledged this in a letter:
With the eight alleged overreporting women removed, the error margin was reduced from 50% to 16% which severely limits its statistical significance. Brind believes the remaining 16% could have resulted from the Swedish fertility registry – where women were interviewed as mothers – which could have increased their tendency to underreport, given that a mother might not want to appear unfit.
The Rookus (1996) study (918 ABC cases/controls) compared two regions in the Netherlands
to assess the effect of religion
on ABC results based on interviews. The secular (western) and conservative
(southeastern) regions showed ABC relative risks of 1.3 (0.7 – 2.6) and 14.6 (1.8 – 120.0) respectively. Although this was a large variance, Brind et al. pointed out that it was attained with an extremely small sample size of 12 cases and 1 control.
Rookus et al. supported their finding with an analysis of how much recall bias existed with oral contraceptive use that could be verified through records. It corroborated the bias, but Brind's et al. letter argues that it only indicated response bias between the two regions, not between case and control subjects within regions. Rookus et al. responded by noting that there was a 4.5 month underreporting difference between control and case subjects in the conservative Catholic region. This was indirect evidence for a reporting bias since women's comfort levels with reporting oral contraception are theoretically higher than induced abortion. Rookus et al. also acknowledged the weakness in the Lindefors-Harris response bias study, but emphasized that more controls (16/59 = 27.1%) than case patients (5/24 = 20.8%) underreported registered induced abortions. They concluded that asserting a causal ABC link would be a disservice to the public and to epidemiological research when "bias has not been ruled out convincingly."
A study by Tang et al. (2000) (225/303 ABC cases/controls) done in Washington State found controls were not more reluctant to report induced abortion than women with breast cancer. Their results were that 14.0% of cases and 14.9% controls (a difference of −0.9%) did not accurately report their abortion history. They do note likely underreporting occurring in certain sub-groups of women; such as older women in a Newcomb study reporting abortions prior to legalization, and a predominantly Roman Catholic
population in the Rookus study.
s) have generally shown no increase in breast cancer risk, although a study by Paoletti concluded there is a "suggestion of increased risk" 1.2 (0.92 – 1.56) after three or more pregnancy losses. Some argue that this apparent lack of effect of miscarriages on breast cancer risk is evidence against the ABC hypothesis, and pro-choice advocates have claimed it is proof that neither early pregnancy loss nor abortion are risk factors for breast cancer.
One of the problems with comparing miscarriage to abortion is the issue of hormone levels in early pregnancy, a key point because the ABC hypothesis rests on hormonal influence over breast tissue development. While it is true most miscarriages are not caused by low hormones, most miscarriages are characterized by low hormone levels. Kunz & Keller (1976) showed that when progesterone
is abnormally low a miscarriage occurs 89% of the time. Advocates of the ABC hypothesis argue that, given the association of most first trimester miscarriages with low hormone levels, spontaneous abortion is not analogous to an induced abortion.
Pro-life organizations like National Right to Life turned to legal tactics that included lobbying against late-term abortions and RU-486. One of the other tactics adopted by the mainstream pro-life movement was promoting an alleged "ABC link". During the height of a publicized "breast cancer epidemic" pro-life organizations began to emphasize preliminary positive ABC results in an effort to further restrict abortion and to discourage women from having abortions. Currently, pro-life organizations lobby to increase obstacles to abortion, such as mandated counseling, waiting periods, and parental notification, and some feel that pro-life advocates treat ABC as simply another tactic in their campaign against abortion. There have been ongoing and incremental legal challenges to abortion in the United States by pro-life groups. In 2005, a Canadian
pro-life organization put up billboard
s in Alberta
with large pink ribbon
s and the statement: "Stop the Cover-Up," in reference to the ABC hypothesis. The Canadian Breast Cancer Foundation
was concerned the billboards misrepresented the state of scientific knowledge on the subject.
The continued focus on the "ABC link" by pro-life groups has created a confrontational political environment. Pro-choice advocates and scientists alike have responded with criticisms. The claims by pro-life advocates are sometimes referred to as pseudoscience
. The extent with which politics has infused the ABC issue is illustrated by an editorial that quoted Daling as saying:
During the late 1990s several United States congressmen became involved in the ABC issue. In 1998, congressman Tom Coburn
questioned a National Cancer Institute (NCI) official on why the NCI website contained out of date information on the ABC issue. Congressman Dave Weldon
wrote a "Dear Colleague" letter to congress in 1999 shortly after the House debated FDA
approval of the abortion drug Mifepristone
; and partially as a result of John Kindley's law review on informed consent which was enclosed. In it Weldon expressed concern that the majority of studies indicate a possible ABC link and the politicization of the ABC issue is "preventing vital information from being given to women."
As of 2006, state law in Alaska
, Mississippi
, Texas
, West Virginia
, and Kansas
requires warning women seeking abortions about a possible breast cancer risk, while Minnesota
reflects the NCI workshop conclusion of no ABC link. Similar legislation
requiring notification has also been introduced, and was pending, in 14 other states
. An editor for the American Journal of Public Health
expressed concern over how such legislative bills propose warnings that do not agree with established scientific findings.
Bioethicist Jacob M. Appel
argues that the mandatory disclosure statutes might be unconstitutional on "rational basis" grounds, because childbirth is significantly more dangerous than abortion, data that is not required in any disclosure law, but which is necessary for a meaningful understanding of risks. According to Appel, "If the roughly fifty million abortions that have occurred in the United States since Roe v. Wade
had all ended in full-term deliveries, approximately five hundred additional women would have died during childbirth."
's (NCI) website. The previous NCI analysis had concluded that while some question regarding an association between abortion and breast cancer existed prior to the mid-1990s, a number of large and well-regarded studies such as Melbye et al. (1997) had resolved the issue; and there was no link between abortion and breast cancer. The Bush administration removed this analysis and replaced it with the following:
This alteration, which suggested that there was scientific uncertainty on the ABC issue, prompted an editorial in the New York Times describing it as an "egregious distortion" and a letter to the Secretary of Health and Human Services from members of Congress. In response to the alteration the NCI convened a three-day consensus workshop entitled Early Reproductive Events and Breast Cancer on February 24–26, 2003. The workshop concluded that induced abortion does not increase a woman's risk of breast cancer, and that the evidence for this was well established. Afterwards, the director of epidemiology research for the American Cancer Society said, “This issue has been resolved scientifically . . . . This is essentially a political debate." Pro-life activist Jill Stanek
put it this way:
Brind was the only one to file a dissenting opinion as a minority report criticizing the NCI's and Melbye's conclusions. Brind alleges the workshop evidence and findings were overly controlled by its organizers since Daling, who has published on the abortion-breast cancer issue, was asked to present on another topic. Further, Melbye submitted unpublished data during the workshop instead of allowing attendees to review it beforehand. Preterm delivery was listed as an epidemiological "gap" even though there was preliminary evidence, by Melbye et al., of a correlation with higher breast cancer risk.
Jasen notes: "A very public target of the anti-abortion movement has been the National Cancer Institute, not only for its dismissal of Daling's findings and uncritical support of Melbye's report, but also for the information supplied on its website, which potentially reaches millions of women around the world." Lawrence R. Huntoon editor-in-chief for the conservative non-mainstream Journal of American Physicians and Surgeons notes in a Malec article that while the workshop had over 100 experts who voted on the findings the NCI website does not elaborate on the vote results.
, North Dakota
alleging false advertising
. The suit alleged the clinic was misleading women by distributing a brochure quoting a National Cancer Institute fact sheet on the ABC issue which stated:
The case was originally scheduled for September 11, 2001, but was delayed as a result of the terrorist attacks
. On March 25, 2002, the trial started and after four days of testimony, Judge Michael McGuire ruled in favor of the clinic. In his decision, he said:
The judge noted it was their "intent" to provide accurate information because the brochure used an outdated 1996 fact sheet that stated there was "no established link", instead of the 1999 fact sheet wording of "inconsistent" evidence for the ABC issue. Linda Rosenthal
, an attorney from the Center for Reproductive Rights characterized the decision thus: "The judge rejected the abortion-breast cancer scare tactic. This ruling should put to rest the unethical, anti-choice scare tactic of using pseudo-science to harass abortion clinics and scare women." John Kindley, one of the lawyers representing Ms. Kjolsrud stated: "I think most citizens, whether they are pro-choice or pro-life, believe in an individual's right to self-determination. They believe people shouldn't be misled and should be told about [procedural] risks, even if there is controversy over those risks." Kindley also wrote an article published in 1998 by the Wisconsin Law Review
outlining the viability of medical malpractice
lawsuits based upon not informing patients considering abortion about the evidence indicating an ABC link.
The decision was appealed and on September 23, 2003, to the North Dakota Supreme Court
which ruled the false advertising law should not have been used by Ms. Kjolsrud. This was because she personally had suffered no injury and hence had no standing (according to North Dakota jurisprudence
) to file the lawsuit on behalf of others. In the appeal, Ms. Kjolsrud "concedes she had not read the brochures before filing her action." However, the appeal also noted that after the lawsuit was filed the abortion clinic updated their brochure to the following:
editorial, Libby Brooks criticized Carroll's study, alleging that the study's methodology was flawed, that the study was funded by an anti-abortion group, and that it was published in a "right wing" journal.
, Chris Mooney argues that "balanced" coverage by the media of the ABC hypothesis, among other scientific hypotheses championed by the religious right, is an example of how the scientific fringe manipulates public opinion by insisting on the illusory notion of journalistic "balance" instead of scientific accuracy. In the article, Mooney criticizes John Carroll
(former Editor-in-Chief of the Los Angeles Times
) for a rebuke Carroll made regarding an article written by Scott Gold about the ABC hypothesis for the L.A. Times. Gold's article covered the National Cancer Institute (NCI) workshop, and Carroll notes that when a scientific advocate (Joel Brind
) for the ABC hypothesis is found:
Carroll's concern is that Gold's article provides fodder to critics who claim that the L.A. Times has a liberal bias. Mooney writes in defense of Gold that:
Responding to criticism Carroll reiterated:
Pro-choice
Pro-life
Abortion
Abortion is defined as the termination of pregnancy by the removal or expulsion from the uterus of a fetus or embryo prior to viability. An abortion can occur spontaneously, in which case it is usually called a miscarriage, or it can be purposely induced...
increases the risk of developing breast cancer
Breast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...
. In early pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
, levels of estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
increase, leading to breast
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
growth in preparation for lactation
Lactation
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...
. The hypothesis proposes that if this process is interrupted by an abortion—before full maturity in the third trimester
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
—then more relatively vulnerable immature cells could be left than there were prior to the pregnancy, resulting in a greater potential risk of breast cancer over time. This mechanism was first proposed and explored in rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
studies conducted in the 1980s.
The abortion–breast cancer hypothesis has been the subject of extensive scientific inquiry, and the scientific community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
has concluded that abortion does not cause breast cancer. This consensus
Scientific consensus
Scientific consensus is the collective judgment, position, and opinion of the community of scientists in a particular field of study. Consensus implies general agreement, though not necessarily unanimity. Scientific consensus is not by itself a scientific argument, and it is not part of the...
is supported by major medical bodies, including the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
, the U.S. National Cancer Institute
National Cancer Institute
The National Cancer Institute is part of the National Institutes of Health , which is one of 11 agencies that are part of the U.S. Department of Health and Human Services. The NCI coordinates the U.S...
, the American Cancer Society
American Cancer Society
The American Cancer Society is the "nationwide community-based voluntary health organization" dedicated, in their own words, "to eliminating cancer as a major health problem by preventing cancer, saving lives, and diminishing suffering from cancer, through research, education, advocacy, and...
, the American College of Obstetricians and Gynecologists, and the Royal College of Obstetricians and Gynaecologists
Royal College of Obstetricians and Gynaecologists
The Royal College of Obstetricians and Gynaecologists is a professional association based in the UK. Its members, including people with and without medical degrees, work in the field of obstetrics and gynaecology, that is, pregnancy, childbirth, and female sexual and reproductive health...
.
Pro-life
Pro-life
Opposition to the legalization of abortion is centered around the pro-life, or anti-abortion, movement, a social and political movement opposing elective abortion on moral grounds and supporting its legal prohibition or restriction...
activists have continued to advance a causal abortion–breast cancer link, and in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
they have sought legal action to present abortion as a cause of breast cancer when counseling women seeking abortion. This political intervention culminated when the George W. Bush Administration
George W. Bush administration
The presidency of George W. Bush began on January 20, 2001, when he was inaugurated as the 43rd President of the United States of America. The oldest son of former president George H. W. Bush, George W...
altered the National Cancer Institute
National Cancer Institute
The National Cancer Institute is part of the National Institutes of Health , which is one of 11 agencies that are part of the U.S. Department of Health and Human Services. The NCI coordinates the U.S...
website to suggest that abortion might cause breast cancer. In response to public concern over this intervention, the NCI convened a 2003 workshop bringing together over 100 experts on the issue. This workshop concluded that while some studies reported a statistical correlation between breast cancer and abortion, the strongest scientific evidence from large prospective
Prospective cohort study
A prospective cohort study is a cohort study that follows over time a group of similar individuals who differ with respect to certain factors under study, to determine how these factors affect rates of a certain outcome...
cohort studies
Cohort study
A cohort study or panel study is a form of longitudinal study used in medicine, social science, actuarial science, and ecology. It is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction...
demonstrates that abortion is not associated with an increase in breast cancer risk, and the positive findings were considered to be due to response bias
Response bias
Response bias is a type of cognitive bias which can affect the results of a statistical survey if respondents answer questions in the way they think the questioner wants them to answer rather than according to their true beliefs...
.
The ongoing promotion of a link between abortion and breast cancer is seen by others as part of the pro-life "woman-centered" strategy against abortion. Pro-life groups maintain they are providing legally necessary informed consent
Informed consent
Informed consent is a phrase often used in law to indicate that the consent a person gives meets certain minimum standards. As a literal matter, in the absence of fraud, it is redundant. An informed consent can be said to have been given based upon a clear appreciation and understanding of the...
, a concern shared by some politically conservative politicians. The abortion–breast cancer issue remains the subject of political controversy.
Views of medical organizations
A number of major medical organizations such as the American Medical AssociationAmerican Medical Association
The American Medical Association , founded in 1847 and incorporated in 1897, is the largest association of medical doctors and medical students in the United States.-Scope and operations:...
, American College of Obstetricians and Gynecologists, World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
and the United States National Cancer Institute
National Cancer Institute
The National Cancer Institute is part of the National Institutes of Health , which is one of 11 agencies that are part of the U.S. Department of Health and Human Services. The NCI coordinates the U.S...
have analyzed larger studies regarding induced abortion and breast cancer. Their uniform conclusion is that there is no causative link between induced abortion and breast cancer.
The American Cancer Society
American Cancer Society
The American Cancer Society is the "nationwide community-based voluntary health organization" dedicated, in their own words, "to eliminating cancer as a major health problem by preventing cancer, saving lives, and diminishing suffering from cancer, through research, education, advocacy, and...
noted with concern that: "The issue of abortion generates passionate viewpoints in many people. Breast cancer is the most common cancer, and is the second leading cancer killer in women (lung cancer is the first). Still, the public is not well-served by false alarms. At this time, the scientific evidence does not support the notion that abortion of any kind raises the risk of breast cancer."
Proponents
Joel BrindJoel Brind
Dr. Joel Brind is a professor, scientist, and a leading advocate of the abortion-breast cancer hypothesis. He is a professor of biology and endocrinology at Baruch College and critiques abortion-breast cancer studies.-Education:...
is a professor of biology and endocrinology
Endocrinology
Endocrinology is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions called hormones, the integration of developmental events such as proliferation, growth, and differentiation and the coordination of...
at Baruch College
Baruch College
Bernard M. Baruch College, more commonly known as Baruch College, is a constituent college of the City University of New York, located in the Flatiron district of Manhattan, New York City. With an acceptance rate of just 23%, Baruch is among the most competitive and diverse colleges in the nation...
and is the primary advocate of an abortion-breast cancer (ABC) link. While Brind is pro-life and his goal to prove an ABC link, he has published papers in respected journals on other human hormone topics. He has fought against the legalization of RU-486 testifying at a federal hearing that "thousands upon thousands" of women would develop breast cancer as a result of using the drug.
In 1996, Brind published a meta-analysis in the Journal of Epidemiology and Community Health (JECH) which was immediately criticized in a Journal of the National Cancer Institute editorial for concluding response bias was unlikely to have affected their results, "dismissal of the study's limitations, and their blurring of association with causation." The amount of attention the study received prompted a cautionary editorial by a JECH editor. After Brind's study failed to convince the scientific community of a causal relationship, Brind co-founded the Breast Cancer Prevention Institute (BCPI) in 1999 with Angela Lanfranchi, a surgeon and pro-life advocate. In 2003, Brind was invited to the NCI workshop, where he was the only one to formally dissent.
Karen Malec, a former teacher and pro-life activist, started the Coalition on Abortion-Breast (CAB) in 1999 with help from Concerned Women for America
Concerned Women for America
Concerned Women for America is a conservative Christian public policy group active in the United States best known for its stance against abortion...
, a conservative Christian U.S. political action group which lobbies for legislation recognizing an abortion-breast cancer link.
Proposed mechanism
Breast tissue contains many lobe
Lobe (anatomy)
In anatomy, a lobe is a clear anatomical division or extension that can be determined without the use of a microscope This is in contrast to a lobule, which is a clear division only visible histologically....
s (segments) and these contain lobules which are groups of breast cells. There are four types of lobules:
- Type 1 has 11 ductulesDuct (anatomy)In anatomy and physiology, a duct is a circumscribed channel leading from an exocrine gland or organ.-Types of ducts:Examples include:-Duct system:...
(immature) - Type 2 has 47 ductules (immature)
- Type 3 has 80 ductules (mature, fewer hormone receptorHormone receptorA hormone receptor is a receptor protein on the surface of a cell or in its interior that binds to a specific hormone. The hormone causes many changes to take place in the cell....
s) - Type 4 are fully matured (cancerCancerCancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
resistant) and contain breast milkBreast milkBreast milk, more specifically human milk, is the milk produced by the breasts of a human female for her infant offspring...
During early pregnancy, type 1 lobules quickly become type 2 lobules because of changes in estrogen and progesterone levels. Maturing into type 3 and then reaching full differentiation
Cellular differentiation
In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...
as type 4 lobules requires an increase of human placental lactogen
Human placental lactogen
Human placental lactogen , also called human chorionic somatomammotropin, is a polypeptide placental hormone. Its structure and function is similar to that of human growth hormone. It modifies the metabolic state of the mother during pregnancy to facilitate the energy supply of the fetus. HPL has...
(hPL) which occurs in the last few months of pregnancy. According to the abortion-breast cancer hypothesis, if an abortion were to interrupt this sequence then it could leave a higher ratio of type 2 lobules than existed prior to the pregnancy. Russo and Russo have shown that mature breast cells have more time for DNA repair
DNA repair
DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
with longer cell cycle
Cell cycle
The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...
s which would account for the reduced risk of parturition against the baseline risk for women who have never conceived and those who have conceived and terminated their pregnancies.
Later on, Russo et al. found that placental human chorionic gonadotropin
Human chorionic gonadotropin
Human chorionic gonadotropin or human chorionic gonadotrophin is a glycoprotein hormone produced during pregnancy that is made by the developing embryo after conception and later by the syncytiotrophoblast .. Some tumors make this hormone; measured elevated levels when the patient is not...
(hCG) induces the synthesis of inhibin by the mammary epithelium. Bernstein et al. independently observed
a reduced breast cancer risk when women were injected with hCG for weight loss or infertility treatment
Assisted reproductive technology
Assisted reproductive technology is a general term referring to methods used to achieve pregnancy by artificial or partially artificial means. It is reproductive technology used primarily in infertility treatments. Some forms of ART are also used in fertile couples for genetic reasons...
. Contrary to the ABC hypothesis, Michaels et al. hypothesize since hCG plays a role in cellular differentiation and may activate apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
, as levels of hCG increase early on in human pregnancy, "an incomplete pregnancy of short duration might impart the benefits of a full-term pregnancy and thus reduce the risk of breast cancer."
Background
The first study involving statistics on abortion and breast cancer was a broad study in 1957, which examined common cancers in JapanJapan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. The researchers were cautious about drawing any conclusions from their unreliable methodologies. During the 1960s several studies by Brian MacMahon
Brian MacMahon
Brian MacMahon was a British-American epidemiologist who chaired the Harvard School of Public Health from 1958 until 1988...
et al. in Europe and Asia touched on a correlation between abortion and breast cancer. Their 1973 paper published in the Journal of the National Cancer Institute inaccurately concluded that "where a relationship was observed, abortion was associated with increased, not decreased, risk." Research relevant to the current ABC discussion focuses on more recent large cohort studies
Cohort study
A cohort study or panel study is a form of longitudinal study used in medicine, social science, actuarial science, and ecology. It is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction...
, a few meta-analyses
Meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...
, many case-control
Case-control
A case-control study is a type of study design in epidemiology. Case-control studies are used to identify factors that may contribute to a medical condition by comparing subjects who have that condition with patients who do not have the condition but are otherwise similar .Case-control studies are...
studies and several early experiments with rats
Laboratory rat
A laboratory rat is a rat of the species Rattus norvegicus which is bred and kept for scientific research. Laboratory rats have served as an important animal model for research in psychology, medicine, and other fields.- Origins :...
.
Rats
Russo & Russo from the Fox Chase Cancer CenterFox Chase Cancer Center
The Fox Chase Cancer Center is a National Cancer Institute-designated Comprehensive Cancer Center research facility and hospital located in the Fox Chase section of Philadelphia, Pennsylvania, United States. The main facilities of the center are located on property adjoining Burholme Park...
in Philadelphia conducted a study in 1980 which examined the proposed correlation between abortion and breast cancer. While analysing the effects of the carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) on the DNA labeling index (DNA-LI) in terminal end buds (TEBs), terminal ducts (TDs) and alveolar buds (ABs) of Sprague-Dawley rats in various stages of reproductive development, they found that rats who had interrupted pregnancies had no noticeable increase in risk for cancer. However, they did find that pregnancy and lactation provided a protective measure against various forms of benign lesions, like hyperplastic alveolar nodules and cysts. While results did suggest that rats who had interrupted pregnancies might be subject to "similar or even higher incidence of benign lesions" than virgin rats, there was no evidence to suggest that abortion would result in a higher incidence of carcinogenesis. A more thorough examination of the phenomenon was conducted in 1982, which confirmed the results. A later study in 1987 further explained their previous findings. After differentiation of the mammary gland
Mammary gland
A mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...
resulting from a full-term pregnancy of the rat, the rate of cell division decreases and the cell cycle length increases, allowing more time for DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
repair
DNA repair
DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
.
Despite the fact that the Russos' studies found similar risk rates between virgin and pregnancy interrupted rats, their research would be used to support the contention that abortion created a greater risk of breast cancer for the next twenty years. In a Discover article sidebar entitled Humans Are Not Rats, Gil Mor, the director of reproductive immunology at the Yale University School of Medicine
Yale University
Yale University is a private, Ivy League university located in New Haven, Connecticut, United States. Founded in 1701 in the Colony of Connecticut, the university is the third-oldest institution of higher education in the United States...
, disagrees with Brind on the importance of the rat studies findings. Mor emphasizes that rat studies are ideal for understanding basic processes but because rats have neither breasts nor breast cancer, people like Brind are on "wobbly" terrain.
Epidemiological studies
The majority of the results in epidemiologyEpidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
are calculated as a relative risk
Relative risk
In statistics and mathematical epidemiology, relative risk is the risk of an event relative to exposure. Relative risk is a ratio of the probability of the event occurring in the exposed group versus a non-exposed group....
, where 1.0 is no risk; results above, like 1.21, is a 21% increased risk and results below, such as 0.8 is a 20% decreased risk. Relative risks are not necessarily significant. To help assess this a relative risk is followed by a confidence interval
Confidence interval
In statistics, a confidence interval is a particular kind of interval estimate of a population parameter and is used to indicate the reliability of an estimate. It is an observed interval , in principle different from sample to sample, that frequently includes the parameter of interest, if the...
in brackets that shows the likelihood (with 95% confidence) that the relative risk is of significance. Any relative risk with a confidence interval that does not include a value of 1 could be considered significant. For example, the confidence intervals (0.3 – 0.9) and (1.5 – 7.8) are statistically significant, whereas the confidence intervals (0.89 – 7.34) or (0.5 – 1.1) are not. With more data the confidence interval becomes smaller; making it an indicator of the result's statistical reliability.
When a relative risk result actually becomes significant is a difficult and contentious issue. As a small result of 1.41 (1.1 – 1.6) even a significant confidence interval (outside 1.0) may be inaccurate because of response bias
Response bias
Response bias is a type of cognitive bias which can affect the results of a statistical survey if respondents answer questions in the way they think the questioner wants them to answer rather than according to their true beliefs...
, incomplete data, missed confounding factors, imprecise controls or statistical analysis. If these possible flaws are accounted for they could change the result and/or the confidence interval impacting its statistical significance.
The number of (X/Y ABC cases/controls) gives X as women in the study who have had abortion(s) (induced and/or spontaneous) with breast cancer and Y is women with breast cancer and no abortion history. This dataset is used when calculating the relative risk and provides a way to compare the size of one study to another.
Confounding factors
There are many confounding factorLurking variable
In statistics, a confounding variable is an extraneous variable in a statistical model that correlates with both the dependent variable and the independent variable...
s for breast cancer. Genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
is a major factor that affects not only a woman's initial breast cancer risk but also her hormonal sensitivity, which in turn affects her susceptibility to a long list of socioeconomic and environmental factors. As Western society
Western world
The Western world, also known as the West and the Occident , is a term referring to the countries of Western Europe , the countries of the Americas, as well all countries of Northern and Central Europe, Australia and New Zealand...
has modernized, environmental
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
carcinogens, delayed child rearing, less breastfeeding
Breastfeeding
Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
, hormone replacement therapy
Hormone replacement therapy (menopause)
Hormone replacement therapy is a system of medical treatment for surgically menopausal, perimenopausal and to a lesser extent postmenopausal women...
(HRT), hormonal contraception
Hormonal contraception
Hormonal contraception refers to birth control methods that act on the endocrine system. Almost all methods are composed of steroid hormones, although in India one selective estrogen receptor modulator is marketed as a contraceptive. The original hormonal method—the combined oral contraceptive...
, early menarche
Menarche
Menarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....
and obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
have increased.
If unaccounted for these factors could obscure any individual variable. Scientific studies remove them using case-control
Case-control
A case-control study is a type of study design in epidemiology. Case-control studies are used to identify factors that may contribute to a medical condition by comparing subjects who have that condition with patients who do not have the condition but are otherwise similar .Case-control studies are...
methodology – a woman who has had an abortion (case) is matched with a very similar woman with no abortion history (control) – if this was not done a study could get a false positive or negative
Type I and type II errors
In statistical test theory the notion of statistical error is an integral part of hypothesis testing. The test requires an unambiguous statement of a null hypothesis, which usually corresponds to a default "state of nature", for example "this person is healthy", "this accused is not guilty" or...
result because of another factor. Examining the ABC issue is all the more difficult because the number of women with an induced abortion history has increased along with other factors in recent decades. Premature birth
Premature birth
In humans preterm birth refers to the birth of a baby of less than 37 weeks gestational age. The cause for preterm birth is in many situations elusive and unknown; many factors appear to be associated with the development of preterm birth, making the reduction of preterm birth a challenging...
adds further complications since uncorroborated studies have indicated it is associated with a history of induced abortion and higher breast cancer risk. One of the most significant controllable factors for breast cancer is parity, or the number of children a women has given birth to. With each full-term pregnancy (particularly the first) the breasts undergo growth and differentiation (in the third trimester); consequently, having no children can increase breast cancer risk.
All of these confounding factors have an effect, directly or indirectly, on hormones which impact breast cancer risk, but they do not significantly affect the results of ABC studies that are properly conducted and take these factors into account with case-control
Case-control
A case-control study is a type of study design in epidemiology. Case-control studies are used to identify factors that may contribute to a medical condition by comparing subjects who have that condition with patients who do not have the condition but are otherwise similar .Case-control studies are...
matching. Hormones being a key factor for cancer risk is well established. Steroidal estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
was added to the U.S. federal carcinogen
Carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
list in December 2002. The American Cancer Society
American Cancer Society
The American Cancer Society is the "nationwide community-based voluntary health organization" dedicated, in their own words, "to eliminating cancer as a major health problem by preventing cancer, saving lives, and diminishing suffering from cancer, through research, education, advocacy, and...
(ACS) and the National Cancer Institute
National Cancer Institute
The National Cancer Institute is part of the National Institutes of Health , which is one of 11 agencies that are part of the U.S. Department of Health and Human Services. The NCI coordinates the U.S...
(NCI) note reproductive hormones can elevate breast cancer risk. In particular a Women's Health Initiative
Women's Health Initiative
The Women's Health Initiative was initiated by the U.S. National Institutes of Health in 1991. The objective of this women's health research initiative was to conduct medical research into some of the major health problems of older women...
hormone replacement therapy study was cut short from an elevated breast cancer and heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
risk using estrogen with progestin
Progestin
A progestin is a synthetic progestogen that has progestinic effects similar to progesterone. The two most common uses of progestins are for hormonal contraception , and to prevent endometrial hyperplasia from unopposed estrogen in hormone replacement therapy...
.
The controversial nature of abortion
Abortion
Abortion is defined as the termination of pregnancy by the removal or expulsion from the uterus of a fetus or embryo prior to viability. An abortion can occur spontaneously, in which case it is usually called a miscarriage, or it can be purposely induced...
may introduce response bias
Response bias
Response bias is a type of cognitive bias which can affect the results of a statistical survey if respondents answer questions in the way they think the questioner wants them to answer rather than according to their true beliefs...
into interview studies, especially for studies done in decades past when abortion was less accepted; however, the statistical significance of bias has yet to be confirmed. In the late 20th century there was some concern of an increase of breast cancer incidence
Incidence (epidemiology)
Incidence is a measure of the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.Incidence proportion is the...
. This was found to be partly due to longer lifespans, and the development of better detection methods capable of finding breast cancer earlier.
Howe
The 1989 study by Holly Howe et al. at the New YorkNew York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
State Department of Health examined young women with breast cancer in upstate New York (100/63 ABC cases/controls). The results indicated an increased 1.9 (1.2 – 3.0) relative risk for induced abortion and 1.5 (0.7 – 3.7) for spontaneous abortion. Although the study had 1451 breast cancer cases the number of individuals with an abortion history was low; consequently the confidence interval is quite large.
The authors believed that the study was inconclusive as fertility patterns were changing dramatically as a result of legal abortion and increased use of contraceptives. Further they did not have a complete reproductive history of younger women who may still have children affecting the results going forward, but Howe et al. concluded it raised new questions for continuing research as women's recorded contraceptive histories grew. Newcomb and Michels point out it examined only very young women and did not account for some confounding factors such as family history of breast cancer.
Lindefors-Harris
Another cohort study by Lindefors-Harris et al. (1989) was done looking at 49,000 women who had received abortions before the age of 30 in Sweden (65 ABC cases – compared with estimate of occurrence in the general population). The relative risk for women who'd given birth previous to the abortion was 0.58 (0.38 – 0.84), whereas women with no births had a relative risk of 1.09 (0.71 – 1.56). The confidence intervals did not establish statistically significant associations between breast cancer and different stages of reproduction, including abortion. Overall, the relative risk was 0.77 (0.58 – 0.99), making for a 23% reduced risk in comparison to "contemporary Swedish population with due consideration to age."The study was funded by Family Health International
Family Health International
Family Health International is a public health and development organization dedicated to improving living standards of the world's most vulnerable people. Family Health International has 2,500 staff conducting research and implementing programs in fifty-five countries...
, a pro-choice NGO
Non-governmental organization
A non-governmental organization is a legally constituted organization created by natural or legal persons that operates independently from any government. The term originated from the United Nations , and is normally used to refer to organizations that do not form part of the government and are...
and although the study started with 49,000 women there were fewer than 5,000 still in the study after 11 years. Lindefors-Harris made no adjustments for family history of breast cancer and the pill, and provides no explanation for a lack of a control group or why the study was limited to women with an abortion before 30 years of age. Brind contends correcting for either of these removes the 23% "protective" effect; and that the study did not account for the difference of nulliparous women in the cohort 41% in comparison to 49% in the general population. Possibly making the protective result about parity (childbearing) rather than abortion.
Melbye
A large, highly regarded ABC study was published by Melbye et al. (1997) of the Statens Serum Institute in CopenhagenCopenhagen
Copenhagen is the capital and largest city of Denmark, with an urban population of 1,199,224 and a metropolitan population of 1,930,260 . With the completion of the transnational Øresund Bridge in 2000, Copenhagen has become the centre of the increasingly integrating Øresund Region...
, which had 1.5 million Danish
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
women in the study's database (1,338 ABC cases, no controls used). Of those women, 280,965 of them had induced abortions recorded in the computerized registry, which was started in 1973 when having an induced abortion through 12 weeks was legal in Denmark. Although there was an observed increased ABC risk with "increasing gestational age of the fetus at the time of the most recent induced abortion"; the overall relative risk after statistical adjustment came to 1.00 (0.94 – 1.06), meaning zero breast cancer risk. This led to the conclusion that "induced abortions have no overall effect on the risk of breast cancer." The Melbye study's conclusions have been used by many organizations, such as NCI, ACOG, ACS, RCOG and Planned Parenthood
Planned Parenthood
Planned Parenthood Federation of America , commonly shortened to Planned Parenthood, is the U.S. affiliate of the International Planned Parenthood Federation and one of its larger members. PPFA is a non-profit organization providing reproductive health and maternal and child health services. The...
, as key scientific evidence of no ABC link.
Brind and Chinchilli had concerns about the Melbye study database as women in the study were born from 1935 to 1978, but the computerized registry of induced abortions only started in 1973. Melbye et al. responded that if the misclassified older women had their risk underestimated, it would be expected that the younger groups would have a higher risk. The statistically adjusted data indicated this was not the case.
However, the statistical adjustments made were another concern of Brind who argues that the Melbye study accidentally adjusted out induced abortion from the overall results. Instead of case-control matching, Melbye el al. decided to manually remove the many confounding factors that increased over time (e.g. smoking, late child bearing, etc.) and were raising breast cancer risk for younger women relative to older women (birth-cohorts). Brind believes finding exactly zero ABC risk was a consequence and red flag indicating ABC risk was removed along with the confounding factors. Melbye et al. found the point to be self-contradictory, considering Brind wanted birth-cohort matching, then argued against "taking birth-cohort differences into account." Brind has stated that he is against the use of just statistical adjustment and that standard case-control
Case-control
A case-control study is a type of study design in epidemiology. Case-control studies are used to identify factors that may contribute to a medical condition by comparing subjects who have that condition with patients who do not have the condition but are otherwise similar .Case-control studies are...
matching may more accurately account for birth-cohort differences.
Another letter to the editor from Senghas and Dolan questioned why a statistically significant result for induced abortions done after 18 weeks gestation was not specifically addressed in the results section of the Melbye study abstract. Melbye et al. explained even though they found the result "interesting and in line with the hypothesis of Russo and Russo, the small number of cases of cancer in women in this category of gestational age prompted us not to overstate the finding." The first section of Table 1 in the Melbye study:
| Week of gestation | No. of Cancers | Person-Years | Relative Risk (95% CI) * | Multivariate Relative Risk (95% CI) † |
|---|---|---|---|---|
| <7 | 36 | 82 000 | 0.81 (0.58–1.13) | 0.81 (0.58–1.13) |
| 7–8 | 526 | 1 012 000 | 1.01 (0.89–1.14) | 1.01 (0.89–1.14) |
| 9–10‡ | 534 | 1 118 000 | 1 | 1 |
| 11–12 | 205 | 422 000 | 1.12 (0.95–1.31) | 1.12 (0.95–1.31) |
| 13–14 | 6 | 14 000 | 1.13 (0.50–2.52) | 1.13 (0.51–2.53) |
| 15–18 | 17 | 35 000 | 1.24 (0.76–2.01) | 1.23 (0.76–2.00) |
| >18 | 14 | 14 000 | 1.92 (1.13–3.26) | 1.89 (1.11–3.22) |
† Values were adjusted for women's age, calendar period, parity, age at delivery of a first child, and the other variables shown in the table.
‡ The women with this characteristic served as the reference group.
Other sections listed age at induced abortion, number of induced abortions, time since induced abortion, and time of induced abortion and live-birth history. There was an indication of a relative risk of 1.29 (0.80–2.08) for 12–19 year olds (relative to 20–24 subcohort), and a protective effect 0.74 (0.41–1.33) for women with an induced abortion before and after their first live birth (relative to induced abortion after 1st live birth subcohort); both results were statistically insignificant.
Michels
A study by Michels et al. (2007) from the Harvard School of Public HealthHarvard School of Public Health
The Harvard School of Public Health is one of the professional graduate schools of Harvard University, located in the Longwood Area of the Boston, Massachusetts neighborhood of Mission Hill, which is next to Harvard Medical School. HSPH is considered a significant school focusing on health in the...
containing 105,716 women (233/1,225 ABC cases/controls) concluded with a relative risk of 1.01 (0.88 – 1.17) "after adjustment for established breast cancer risk factors." Some of the results lead the authors to stipulate: "Although our data are not compatible with any substantial overall relation between induced abortion and breast cancer, we cannot exclude a modest association in subgroups defined by known breast cancer risk factors, timing of abortion, or parity." This modest association was mostly not statistically significant.
Further cohort studies
Several other recent prospective cohort studiesCohort study
A cohort study or panel study is a form of longitudinal study used in medicine, social science, actuarial science, and ecology. It is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction...
have also found little evidence of a link between induced abortion and breast cancer. A study of 267,361 European women (746/2,908 ABC cases/controls), published in 2006, found no significant ABC risk. Another 2006 study involving 267,400 women (872/771 ABC cases/controls) in Shanghai
Shanghai
Shanghai is the largest city by population in China and the largest city proper in the world. It is one of the four province-level municipalities in the People's Republic of China, with a total population of over 23 million as of 2010...
found no evidence of an ABC link. The Shanghai study also noted that women who had an abortion were at a significantly decreased risk of uterine cancer.
Beral
In March 2004, Beral et al. published a study in The LancetThe Lancet
The Lancet is a weekly peer-reviewed general medical journal. It is one of the world's best known, oldest, and most respected general medical journals...
as a collaborative reanalysis on Breast cancer and abortion. This meta-analysis of 53 epidemiologic studies of 83,000 women with breast cancer undertaken in 16 countries did not find evidence of a relationship between induced abortion and breast cancer, with a relative risk of 0.93 (0.89 – 0.96). Organizations and media outlets referenced the Beral study as the most comprehensive overview of the ABC evidence.
Brind maintains that like meta-analysis this study is subject to selection bias
Selection bias
Selection bias is a statistical bias in which there is an error in choosing the individuals or groups to take part in a scientific study. It is sometimes referred to as the selection effect. The term "selection bias" most often refers to the distortion of a statistical analysis, resulting from the...
, which he believes is reflected in the removal of 15 published, peer-reviewed studies with positive ABC results for "unscientific reasons"; and including 28 unpublished studies that outnumber the remaining 24 peer reviewed studies. Beral refers to the Lindefors-Harris response bias study as an explanation for higher ABC risk found in interview based studies, however Brind notes in 1998 that Lindefors-Harris conceded their initial conclusion may have been unsound.
Brind
Brind et al. (1996) conducted a meta-analysis of 23 epidemiologic studies. It calculated that there was on average a relative risk of 1.3 (1.2 – 1.4) increased risk of breast cancer. The meta-analysis was criticized for selection biasSelection bias
Selection bias is a statistical bias in which there is an error in choosing the individuals or groups to take part in a scientific study. It is sometimes referred to as the selection effect. The term "selection bias" most often refers to the distortion of a statistical analysis, resulting from the...
by using studies with widely varying results, using different types of studies, not working with the raw data from several studies, and including studies that have possible methodological weaknesses.
The strong reaction to the study particularly in Britain and the United States prompted the editor-in-chief Stuart Donnan to write an editorial. In it he notes:
However, in the light of recent unease about appropriate but open communication of risks associated with oral contraceptive pills, it will surely be agreed that open discussion of risks
is vital and must include the people – in this case the women – concerned. I believe that if you take a view (as I do), which is often called 'pro-choice', you need at the same time to have a view which might be called 'pro-information' without excessive paternalistic censorship (or interpretation) of the data.
The Royal College of Obstetricians and Gynaecologists
Royal College of Obstetricians and Gynaecologists
The Royal College of Obstetricians and Gynaecologists is a professional association based in the UK. Its members, including people with and without medical degrees, work in the field of obstetrics and gynaecology, that is, pregnancy, childbirth, and female sexual and reproductive health...
(RCOG) in March 2000 published evidence-based guidelines on women requesting induced abortion. The review of the available evidence at the time was "inconclusive" regarding the ABC link. They also noted "Brind's paper had no methodological shortcomings and could not be disregarded." However, in 2003 the RCOG concluded that there was no link between abortion and breast cancer. Some of the ABC studies RCOG reference as evidence (pg. 77) have been heavily criticized by Brind in 2005.
Interviews
Interview (case-control) based studies have been inconsistent on the ABC hypothesis. With the small numbers involved in each individual study and the possibility that recall bias skewed the results, recent focus has switched to meta-analysis and record based studies which are typically much larger. Included are a few interview studies of note.Daling
Janet Daling from the Fred Hutchinson Cancer Research CenterFred Hutchinson Cancer Research Center
The Fred Hutchinson Cancer Research Center, is one of the world’s leading cancer research institutes...
headed two studies on the ABC issue looking at women in Washington state. The 1994 study (845/961 ABC cases/controls) results indicated an associated relative risk of 1.5 (1.2 – 1.9) among women who had given birth before having an abortion. This was reflected in higher risks for women younger than 18 or older than 30 years of age who have had abortions after 8 weeks' gestation. Their conclusion emphasized that although the evidence suggested the possibility of a correlative relationship, their findings were not consistent enough to establish one.
The second larger study Daling conducted in 1996 (1,302/1,180 ABC cases/controls) found that abortion was associated with a relative risk value of 1.2 (1.0 – 1.5). The study also found a significant relative risk of 2.0 (1.2 – 3.3) for nulliparous women with an induced abortion at less than 8 weeks gestation. Daling et al. concluded that:
Daling et al. examined the possibility of response bias by comparing results from two recent studies on invasive cervical cancer and ovarian cancer. The results argued against significant response bias. However, Rookus (1996) study noted that patients with cervical cancer may report differently than breast cancer patients.
Further interview studies
A 2001 study (1,459/1,556 ABC cases/controls) conducted in ShanghaiShanghai
Shanghai is the largest city by population in China and the largest city proper in the world. It is one of the four province-level municipalities in the People's Republic of China, with a total population of over 23 million as of 2010...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
by Sanderson et al. from the University of South Carolina
University of South Carolina
The University of South Carolina is a public, co-educational research university located in Columbia, South Carolina, United States, with 7 surrounding satellite campuses. Its historic campus covers over in downtown Columbia not far from the South Carolina State House...
and South Carolina Cancer Center at Columbia
Columbia, South Carolina
Columbia is the state capital and largest city in the U.S. state of South Carolina. The population was 129,272 according to the 2010 census. Columbia is the county seat of Richland County, but a portion of the city extends into neighboring Lexington County. The city is the center of a metropolitan...
concluded that there was no ABC link and that multiple abortions did not put one at greater risk. Since induced abortion is common, legal, and even mandated by the government in China, the recall bias was minimized. Brind has argued that the same factors that make the Chinese study ideal for reducing recall bias also makes them inappropriate for comparison to the West. Specifically, with China’s strict population control, the vast majority of the abortions in the Chinese study were done after the first full-term pregnancy. This differs from North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
The Istanbul University
Istanbul University
Istanbul University is a Turkish university located in Istanbul. The main campus is adjacent to Beyazıt Square.- Synopsis :A madrasa, a religious school, was established sometime in the 15th century after the Ottoman conquest of Constantinople. An institution of higher education named the...
Medical Faculty published a study in 2009 (742/930 ABC cases/controls) of outpatients from clinics, authored by Ozmen et al. it found a 1.31 (1.13 – 1.53) increased ABC risk. The authors point out various potential biases such as selection
Selection bias
Selection bias is a statistical bias in which there is an error in choosing the individuals or groups to take part in a scientific study. It is sometimes referred to as the selection effect. The term "selection bias" most often refers to the distortion of a statistical analysis, resulting from the...
, information
Information bias (epidemiology)
-Definition:Also referred to as observational bias and misclassification. A Dictionary of Epidemiology, sponsored by the International Epidemiological Association, defines this as the following:...
and even hospital admission bias may have impacted their results. They believe the large pool of patients available to them and the resulting large size of the study "provided reasonably stable risk estimates."
Response bias
Response biasResponse bias
Response bias is a type of cognitive bias which can affect the results of a statistical survey if respondents answer questions in the way they think the questioner wants them to answer rather than according to their true beliefs...
occurs when women intentionally "underreport" their abortion history, meaning that they deny having an abortion or claim to have fewer abortions than they actually had. This can happen because of the personal and controversial nature of abortion, which may cause women to not want to provide full disclosure. Women in control groups are less likely to have serious illnesses, and hence have less motivation to be truthful than those trying to diagnose their problem. When this occurs, it artificially creates an ABC link where none exists. Three major studies have been published examining abortion response bias.
An editorial by Weed and Kramer focused on how Brind's meta-analysis dismissed bias as a factor. The editorial cites the Lindefors-Harris response bias study that used a "registry-based gold standard to show that healthy women consistently and widely underreport their history of abortion." Weed and Kramer considered this compelling evidence there could be systematic bias within the studies included in the meta-analysis. However, subsequently the Lindefors-Harris conclusion was quietly retracted in 1998. Weed and Kramer believed a causal conclusion was a "leap beyond the bounds of inference" and concluded:
Because bias impedes our vision and is subject to sound inquiry, we are far from reaching a scientific "limit". Indeed, after this excursion into the issue of abortion, bias, and breast cancer, it seems our future has as much to do with human behavior as with human biology.
A review of ABC studies was conducted by Bartholomew in 1998. It concluded that if studies least susceptible to response bias are considered, they suggest there is no association between abortion and breast cancer. Chris Kahlenborn, M.D., a pro-life researcher and specialist in internal medicine, observes in his book Breast Cancer: Its Link to Abortion and the Birth Control Pill that if report bias were a significant factor in interview-based studies, then:
... thousands of other studies in medicine might now be deemed 'worthless.' Every time one had a disease or 'effect' that was caused by a controversial risk factor (i.e., one of the causes), the study might be considered invalid based upon 'recall bias.'
Lindefors-Harris
The Lindefors-Harris (1991) study (317/512 ABC cases/controls) was the first major study to examine response and recall bias. It used the data of two independent Swedish
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
induced abortion studies, and concluded there was a 1.5 (1.1 – 2.1) margin of error due to recall bias. However, eight women (seven cases, one control) included in this error margin apparently "overreported" their abortions, meaning the women reported having an abortion that was not reflected in the records. It was decided that for the purposes of the study, these women did not have abortions.
The 1994 Daling study examined the findings on overreporting of the Lindefors-Harris study and found it "reasonable to assume that virtually no women who truly did not have an abortion would claim to have had one." In 1998 the co-authors of the Lindefors-Harris study acknowledged this in a letter:
We are not surprised to find some Swedish women confidentially reporting having had induced abortions during the period 1966–1974 that are not recorded as legally induced abortions. It is plausible that such induced abortions are more susceptible to recall bias than induced abortions performed within the legal context in Sweden.
With the eight alleged overreporting women removed, the error margin was reduced from 50% to 16% which severely limits its statistical significance. Brind believes the remaining 16% could have resulted from the Swedish fertility registry – where women were interviewed as mothers – which could have increased their tendency to underreport, given that a mother might not want to appear unfit.
Rookus
The Rookus (1996) study (918 ABC cases/controls) compared two regions in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
to assess the effect of religion
Religion
Religion is a collection of cultural systems, belief systems, and worldviews that establishes symbols that relate humanity to spirituality and, sometimes, to moral values. Many religions have narratives, symbols, traditions and sacred histories that are intended to give meaning to life or to...
on ABC results based on interviews. The secular (western) and conservative
Social conservatism
Social Conservatism is primarily a political, and usually morally influenced, ideology that focuses on the preservation of what are seen as traditional values. Social conservatism is a form of authoritarianism often associated with the position that the federal government should have a greater role...
(southeastern) regions showed ABC relative risks of 1.3 (0.7 – 2.6) and 14.6 (1.8 – 120.0) respectively. Although this was a large variance, Brind et al. pointed out that it was attained with an extremely small sample size of 12 cases and 1 control.
Rookus et al. supported their finding with an analysis of how much recall bias existed with oral contraceptive use that could be verified through records. It corroborated the bias, but Brind's et al. letter argues that it only indicated response bias between the two regions, not between case and control subjects within regions. Rookus et al. responded by noting that there was a 4.5 month underreporting difference between control and case subjects in the conservative Catholic region. This was indirect evidence for a reporting bias since women's comfort levels with reporting oral contraception are theoretically higher than induced abortion. Rookus et al. also acknowledged the weakness in the Lindefors-Harris response bias study, but emphasized that more controls (16/59 = 27.1%) than case patients (5/24 = 20.8%) underreported registered induced abortions. They concluded that asserting a causal ABC link would be a disservice to the public and to epidemiological research when "bias has not been ruled out convincingly."
Tang
A study by Tang et al. (2000) (225/303 ABC cases/controls) done in Washington State found controls were not more reluctant to report induced abortion than women with breast cancer. Their results were that 14.0% of cases and 14.9% controls (a difference of −0.9%) did not accurately report their abortion history. They do note likely underreporting occurring in certain sub-groups of women; such as older women in a Newcomb study reporting abortions prior to legalization, and a predominantly Roman Catholic
Roman Catholic Church
The Catholic Church, also known as the Roman Catholic Church, is the world's largest Christian church, with over a billion members. Led by the Pope, it defines its mission as spreading the gospel of Jesus Christ, administering the sacraments and exercising charity...
population in the Rookus study.
Spontaneous abortion
Studies of spontaneous abortions (miscarriageMiscarriage
Miscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving independently, generally defined in humans at prior to 20 weeks of gestation...
s) have generally shown no increase in breast cancer risk, although a study by Paoletti concluded there is a "suggestion of increased risk" 1.2 (0.92 – 1.56) after three or more pregnancy losses. Some argue that this apparent lack of effect of miscarriages on breast cancer risk is evidence against the ABC hypothesis, and pro-choice advocates have claimed it is proof that neither early pregnancy loss nor abortion are risk factors for breast cancer.
One of the problems with comparing miscarriage to abortion is the issue of hormone levels in early pregnancy, a key point because the ABC hypothesis rests on hormonal influence over breast tissue development. While it is true most miscarriages are not caused by low hormones, most miscarriages are characterized by low hormone levels. Kunz & Keller (1976) showed that when progesterone
Progesterone
Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...
is abnormally low a miscarriage occurs 89% of the time. Advocates of the ABC hypothesis argue that, given the association of most first trimester miscarriages with low hormone levels, spontaneous abortion is not analogous to an induced abortion.
Politicization
Public interest in an association between abortion and breast cancer coincided with the rise of the militant pro-life movement which turned to violence. After the 1993 murder of physician David Gunn by a pro-life activist, mainstream pro-life organizations disavowed violent methods.Pro-life organizations like National Right to Life turned to legal tactics that included lobbying against late-term abortions and RU-486. One of the other tactics adopted by the mainstream pro-life movement was promoting an alleged "ABC link". During the height of a publicized "breast cancer epidemic" pro-life organizations began to emphasize preliminary positive ABC results in an effort to further restrict abortion and to discourage women from having abortions. Currently, pro-life organizations lobby to increase obstacles to abortion, such as mandated counseling, waiting periods, and parental notification, and some feel that pro-life advocates treat ABC as simply another tactic in their campaign against abortion. There have been ongoing and incremental legal challenges to abortion in the United States by pro-life groups. In 2005, a Canadian
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
pro-life organization put up billboard
Billboard (advertising)
A billboard is a large outdoor advertising structure , typically found in high traffic areas such as alongside busy roads. Billboards present large advertisements to passing pedestrians and drivers...
s in Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
with large pink ribbon
Pink ribbon
The pink ribbon is an international symbol of breast cancer awareness. Pink ribbons, and the color pink in general, identify the wearer or promoter with the breast cancer brand and express moral support for women with breast cancer....
s and the statement: "Stop the Cover-Up," in reference to the ABC hypothesis. The Canadian Breast Cancer Foundation
Canadian Breast Cancer Foundation
The Canadian Breast Cancer Foundation is a charitable organization which raises money to advance research, education, diagnosis and treatment of breast cancer. Established in 1986, it works to fund, support, and advocate for education and awareness programs, early diagnosis and treatment of breast...
was concerned the billboards misrepresented the state of scientific knowledge on the subject.
The continued focus on the "ABC link" by pro-life groups has created a confrontational political environment. Pro-choice advocates and scientists alike have responded with criticisms. The claims by pro-life advocates are sometimes referred to as pseudoscience
Pseudoscience
Pseudoscience is a claim, belief, or practice which is presented as scientific, but which does not adhere to a valid scientific method, lacks supporting evidence or plausibility, cannot be reliably tested, or otherwise lacks scientific status...
. The extent with which politics has infused the ABC issue is illustrated by an editorial that quoted Daling as saying:
During the late 1990s several United States congressmen became involved in the ABC issue. In 1998, congressman Tom Coburn
Tom Coburn
Thomas Allen "Tom" Coburn, M.D. , is an American politician, medical doctor, and Southern Baptist deacon. A member of the Republican Party, he currently serves as the junior U.S. Senator from Oklahoma. In the Senate, he is known as "Dr. No" for his tendency to place holds on and vote against bills...
questioned a National Cancer Institute (NCI) official on why the NCI website contained out of date information on the ABC issue. Congressman Dave Weldon
Dave Weldon
David Joseph Weldon, is an American politician and physician. He was a Republican member of the United States House of Representatives, representing .-Early life:...
wrote a "Dear Colleague" letter to congress in 1999 shortly after the House debated FDA
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
approval of the abortion drug Mifepristone
Mifepristone
Mifepristone is a synthetic steroid compound used as a pharmaceutical. It is a progesterone receptor antagonist used as an abortifacient in the first months of pregnancy, and in smaller doses as an emergency contraceptive. During early trials, it was known as RU-38486 or simply RU-486, its...
; and partially as a result of John Kindley's law review on informed consent which was enclosed. In it Weldon expressed concern that the majority of studies indicate a possible ABC link and the politicization of the ABC issue is "preventing vital information from being given to women."
As of 2006, state law in Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, Mississippi
Mississippi
Mississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...
, Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...
, and Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
requires warning women seeking abortions about a possible breast cancer risk, while Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
reflects the NCI workshop conclusion of no ABC link. Similar legislation
Legislation
Legislation is law which has been promulgated by a legislature or other governing body, or the process of making it...
requiring notification has also been introduced, and was pending, in 14 other states
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
. An editor for the American Journal of Public Health
American Journal of Public Health
The American Journal of Public Health is a monthly peer-reviewed medical journal published by the American Public Health Association covering health policy and public health. The journal was established in 1911 and its stated mission is "to advance public health research, policy, practice, and...
expressed concern over how such legislative bills propose warnings that do not agree with established scientific findings.
Bioethicist Jacob M. Appel
Jacob M. Appel
Jacob M. Appel is an American author, bioethicist and social critic. He is best known for his short stories, his work as a playwright, and his writing in the fields of reproductive ethics, organ donation, neuroethics and euthanasia....
argues that the mandatory disclosure statutes might be unconstitutional on "rational basis" grounds, because childbirth is significantly more dangerous than abortion, data that is not required in any disclosure law, but which is necessary for a meaningful understanding of risks. According to Appel, "If the roughly fifty million abortions that have occurred in the United States since Roe v. Wade
Roe v. Wade
Roe v. Wade, , was a controversial landmark decision by the United States Supreme Court on the issue of abortion. The Court decided that a right to privacy under the due process clause in the Fourteenth Amendment to the United States Constitution extends to a woman's decision to have an abortion,...
had all ended in full-term deliveries, approximately five hundred additional women would have died during childbirth."
National Cancer Institute
A report from the Committee on Oversight and Government Reform found that in November 2002, the Bush administration altered the National Cancer InstituteNational Cancer Institute
The National Cancer Institute is part of the National Institutes of Health , which is one of 11 agencies that are part of the U.S. Department of Health and Human Services. The NCI coordinates the U.S...
's (NCI) website. The previous NCI analysis had concluded that while some question regarding an association between abortion and breast cancer existed prior to the mid-1990s, a number of large and well-regarded studies such as Melbye et al. (1997) had resolved the issue; and there was no link between abortion and breast cancer. The Bush administration removed this analysis and replaced it with the following:
This alteration, which suggested that there was scientific uncertainty on the ABC issue, prompted an editorial in the New York Times describing it as an "egregious distortion" and a letter to the Secretary of Health and Human Services from members of Congress. In response to the alteration the NCI convened a three-day consensus workshop entitled Early Reproductive Events and Breast Cancer on February 24–26, 2003. The workshop concluded that induced abortion does not increase a woman's risk of breast cancer, and that the evidence for this was well established. Afterwards, the director of epidemiology research for the American Cancer Society said, “This issue has been resolved scientifically . . . . This is essentially a political debate." Pro-life activist Jill Stanek
Jill Stanek
Jill Stanek is an American pro-life activist from Illinois, best known for her allegations regarding "live birth abortions" that she publicly testified were being performed at Christ Hospital in the Chicago suburb of Oak Lawn...
put it this way:
Brind was the only one to file a dissenting opinion as a minority report criticizing the NCI's and Melbye's conclusions. Brind alleges the workshop evidence and findings were overly controlled by its organizers since Daling, who has published on the abortion-breast cancer issue, was asked to present on another topic. Further, Melbye submitted unpublished data during the workshop instead of allowing attendees to review it beforehand. Preterm delivery was listed as an epidemiological "gap" even though there was preliminary evidence, by Melbye et al., of a correlation with higher breast cancer risk.
Jasen notes: "A very public target of the anti-abortion movement has been the National Cancer Institute, not only for its dismissal of Daling's findings and uncritical support of Melbye's report, but also for the information supplied on its website, which potentially reaches millions of women around the world." Lawrence R. Huntoon editor-in-chief for the conservative non-mainstream Journal of American Physicians and Surgeons notes in a Malec article that while the workshop had over 100 experts who voted on the findings the NCI website does not elaborate on the vote results.
North Dakota lawsuit
One example of the politicization of science is the case of Kjolsrud v. MKB Management Corporation. In January 2000, Amy Jo Kjolsrud (née Mattson), a pro-life counselor, sued the Red River Women's Clinic in FargoFargo, North Dakota
Fargo is the largest city in the U.S. state of North Dakota and the county seat of Cass County. In 2010, its population was 105,549, and it had an estimated metropolitan population of 208,777...
, North Dakota
North Dakota
North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
alleging false advertising
Advertising
Advertising is a form of communication used to persuade an audience to take some action with respect to products, ideas, or services. Most commonly, the desired result is to drive consumer behavior with respect to a commercial offering, although political and ideological advertising is also common...
. The suit alleged the clinic was misleading women by distributing a brochure quoting a National Cancer Institute fact sheet on the ABC issue which stated:
- "Anti-abortion activists claim that having an abortion increases the risk of developing breast cancer and endangers future childbearing. None of these claims are supported by medical research or established medical organizations." (emphasis in original)
The case was originally scheduled for September 11, 2001, but was delayed as a result of the terrorist attacks
September 11, 2001 attacks
The September 11 attacks The September 11 attacks The September 11 attacks (also referred to as September 11, September 11th or 9/119/11 is pronounced "nine eleven". The slash is not part of the pronunciation...
. On March 25, 2002, the trial started and after four days of testimony, Judge Michael McGuire ruled in favor of the clinic. In his decision, he said:
The judge noted it was their "intent" to provide accurate information because the brochure used an outdated 1996 fact sheet that stated there was "no established link", instead of the 1999 fact sheet wording of "inconsistent" evidence for the ABC issue. Linda Rosenthal
Linda Rosenthal
Linda B. Rosenthal represents District 67 as a Democrat in the New York State Assembly, which includes parts of Manhattan's Upper West Side and Clinton neighborhoods....
, an attorney from the Center for Reproductive Rights characterized the decision thus: "The judge rejected the abortion-breast cancer scare tactic. This ruling should put to rest the unethical, anti-choice scare tactic of using pseudo-science to harass abortion clinics and scare women." John Kindley, one of the lawyers representing Ms. Kjolsrud stated: "I think most citizens, whether they are pro-choice or pro-life, believe in an individual's right to self-determination. They believe people shouldn't be misled and should be told about [procedural] risks, even if there is controversy over those risks." Kindley also wrote an article published in 1998 by the Wisconsin Law Review
Wisconsin Law Review
The Wisconsin Law Review is the principal journal of legal commentary and analysis published by students at the University of Wisconsin Law School.- History :...
outlining the viability of medical malpractice
Medical malpractice
Medical malpractice is professional negligence by act or omission by a health care provider in which the treatment provided falls below the accepted standard of practice in the medical community and causes injury or death to the patient, with most cases involving medical error. Standards and...
lawsuits based upon not informing patients considering abortion about the evidence indicating an ABC link.
The decision was appealed and on September 23, 2003, to the North Dakota Supreme Court
North Dakota Supreme Court
The North Dakota Supreme Court is the highest court of law in the state of North Dakota. The Court rules on questions of law in appeals from the state's district courts....
which ruled the false advertising law should not have been used by Ms. Kjolsrud. This was because she personally had suffered no injury and hence had no standing (according to North Dakota jurisprudence
Jurisprudence
Jurisprudence is the theory and philosophy of law. Scholars of jurisprudence, or legal theorists , hope to obtain a deeper understanding of the nature of law, of legal reasoning, legal systems and of legal institutions...
) to file the lawsuit on behalf of others. In the appeal, Ms. Kjolsrud "concedes she had not read the brochures before filing her action." However, the appeal also noted that after the lawsuit was filed the abortion clinic updated their brochure to the following:
- "Some anti-abortion activists claim that having an abortion increases the risk of developing breast cancer. A substantial body of medical research indicates that there is no established link between abortion and breast cancer. In fact, the National Cancer Institute has stated, '[t]here is no evidence of a direct relationship between breast cancer and either induced or spontaneous abortion.'"
Carroll
In the Fall of 2007, Patrick S. Carroll published a statistical analysis in the Journal of American Physicians and Surgeons, a politically conservative journal with a pro-life stance. The study claimed that, among seven risk factors, abortion was the "best predictor of breast cancer," and fertility was also a useful predictor. It forecasts, for the year 2025, higher breast cancer rates for Czech Republic, England and Sweden and lower for Finland and Denmark based on abortion trends. In a GuardianThe Guardian
The Guardian, formerly known as The Manchester Guardian , is a British national daily newspaper in the Berliner format...
editorial, Libby Brooks criticized Carroll's study, alleging that the study's methodology was flawed, that the study was funded by an anti-abortion group, and that it was published in a "right wing" journal.
Criticism of media coverage
In an article entitled "Blinded by Science" for the Columbia Journalism ReviewColumbia Journalism Review
The Columbia Journalism Review is an American magazine for professional journalists published bimonthly by the Columbia University Graduate School of Journalism since 1961....
, Chris Mooney argues that "balanced" coverage by the media of the ABC hypothesis, among other scientific hypotheses championed by the religious right, is an example of how the scientific fringe manipulates public opinion by insisting on the illusory notion of journalistic "balance" instead of scientific accuracy. In the article, Mooney criticizes John Carroll
John Carroll (journalist)
John S. Carroll was the editor of the Los Angeles Times and The Baltimore Sun. During his tenure the Times won 13 Pulitzer Prizes.-Early career:...
(former Editor-in-Chief of the Los Angeles Times
Los Angeles Times
The Los Angeles Times is a daily newspaper published in Los Angeles, California, since 1881. It was the second-largest metropolitan newspaper in circulation in the United States in 2008 and the fourth most widely distributed newspaper in the country....
) for a rebuke Carroll made regarding an article written by Scott Gold about the ABC hypothesis for the L.A. Times. Gold's article covered the National Cancer Institute (NCI) workshop, and Carroll notes that when a scientific advocate (Joel Brind
Joel Brind
Dr. Joel Brind is a professor, scientist, and a leading advocate of the abortion-breast cancer hypothesis. He is a professor of biology and endocrinology at Baruch College and critiques abortion-breast cancer studies.-Education:...
) for the ABC hypothesis is found:
It is not until the last three paragraphs of the story that we finally surface a professor of biology and endocrinology who believes the abortion/cancer connection is valid. But do we quote him as to why he believes this? No. We quote his political views.
Apparently the scientific argument for the anti-abortion side is so absurd that we don't need to waste our readers' time with it.
Carroll's concern is that Gold's article provides fodder to critics who claim that the L.A. Times has a liberal bias. Mooney writes in defense of Gold that:
As a general rule, journalists should treat fringe scientific claims with considerable skepticism, and find out what major peer-reviewed papers or assessments have to say about them. Moreover, they should adhere to the principle that the more outlandish or dramatic the claim, the more skepticism it warrants. The Los Angeles Times’s Carroll observes that “every good journalist has a bit of a contrarian in his soul,” but it is precisely this impulse that can lead reporters astray. The fact is, nonscientist journalists can all too easily fall for scientific-sounding claims that they can’t adequately evaluate on their own.
Responding to criticism Carroll reiterated:
You have an obligation to find a scientist, and if the scientist has something to say, then you can subject the scientist’s views to rigorous examination.
External links
Scientific community and mainstream media- National Cancer Institute: Abortion, Miscarriage, and Breast Cancer Risk
- Induced abortion does not increase breast cancer risk, a fact sheet from the World Health OrganizationWorld Health OrganizationThe World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
- Is Abortion Linked to Breast Cancer? from the American Cancer SocietyAmerican Cancer SocietyThe American Cancer Society is the "nationwide community-based voluntary health organization" dedicated, in their own words, "to eliminating cancer as a major health problem by preventing cancer, saving lives, and diminishing suffering from cancer, through research, education, advocacy, and...
- American College of Obstetricians and Gynecologists: Finds No Link Between Abortion and Breast Cancer Risk
- The Care of Women Requesting Induced Abortion, from the Royal College of Obstetricians and GynaecologistsRoyal College of Obstetricians and GynaecologistsThe Royal College of Obstetricians and Gynaecologists is a professional association based in the UK. Its members, including people with and without medical degrees, work in the field of obstetrics and gynaecology, that is, pregnancy, childbirth, and female sexual and reproductive health...
- Discover Magazine: The Scientist Who Hated Abortion by Barry Yeoman
- Factors That Do Not Increase Risk from the Susan G. Komen Foundation
Pro-choice
- Planned Parenthood: Anti-choice Claims About Abortion and Breast Cancer
- Center for Reproductive Rights: False Claims of Breast Cancer Risk
- National Abortion Federation: The Abortion and Breast Cancer Myth
Pro-life