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Ovarian cancer
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Ovarian cancer is a cancerous growth arising from an ovary. Although ovarian cancer is known to occur in many species, the majority of the medical literature and the focus of this article is on ovarian cancer in humans.
Ovarian cancer most commonly thought to form in the lining of the ovary (resulting in epithelial ovarian cancer) or in the egg cells (resulting in a germ cell tumor). However, recent evidence points towards the Fallopian tube as precursor for ovarian cancers
Ovarian cancer is the fifth leading cause of death from cancer in women and the leading cause of death from gynecological cancer.
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Encyclopedia
Ovarian cancer is a cancerous growth arising from an ovary. Although ovarian cancer is known to occur in many species, the majority of the medical literature and the focus of this article is on ovarian cancer in humans.
Ovarian cancer most commonly thought to form in the lining of the ovary (resulting in epithelial ovarian cancer) or in the egg cells (resulting in a germ cell tumor). However, recent evidence points towards the Fallopian tube as precursor for ovarian cancers
Ovarian cancer is the fifth leading cause of death from cancer in women and the leading cause of death from gynecological cancer. A woman has a lifetime risk of ovarian cancer of around 1.5%, which makes it the second most common gynecologic malignancy (the first being breast cancer).
Ovarian cancer has been named 'the silent killer' because it frequently causes non-specific symptoms, which contribute to diagnostic delay, diagnosis in a late stage and a poor prognosis. Most women with ovarian cancer report one or more symptoms such as abdominal pain or discomfort, an abdominal mass, bloating, back pain, urinary urgency, constipation, tiredness and a range of other non-specific symptoms, as well as more specific symptoms such as pelvic pain, abnormal vaginal bleeding or involuntary weight loss. There can be a build-up of fluid in the abdominal cavity (this is called ascites).
The diagnosis of ovarian cancer can be suspected from an abnormal physical examination (including a pelvic examination), a blood test (for CA-125, more specifically) or from medical imaging studies. The diagnosis can be confirmed with a surgical procedure (open or keyhole surgery) to inspect the abdominal cavity, take biopsies (tissue samples for microscopic analysis) and look for cancer cells in the abdominal fluid. Treatment usually involves chemotherapy and surgery, and sometimes radiotherapy.
In most cases, the cause of ovarian cancer remains unknown. There is an increased risk of ovarian cancer in older women and in those who have a first or second degree relative with the disease. Hereditary forms of ovarian cancer can be caused by mutations in specific genes (most notably BRCA1 and BRCA2, but also in genes for hereditary nonpolyposis colorectal cancer). Infertile women and those with a condition called endometriosis, those who have never been pregnant and those who use postmenopausal estrogen replacement therapy are at increased risk. Use of oral contraceptive pills is a protective factor. The risk is also lower in women who have had their uterine tubes blocked surgically (tubal ligation).
Epidemiology
The exact cause is usually unknown. The disease is more common in industrialized nations, with the exception of Japan. In the United States, females have a 1.4% to 2.5% (1 out of 40-60 women) lifetime chance of developing ovarian cancer. Older women are at highest risk. More than half of the deaths from ovarian cancer occur in women between 55 and 74 years of age and approximately one quarter of ovarian cancer deaths occur in women between 35 and 54 years of age.
The risk of developing ovarian cancer appears to be affected by several factors. The more children a woman has, the lower her risk of ovarian cancer. Early age at first pregnancy, older ages of final pregnancy and the use of low dose hormonal contraception have also been shown to have a protective effect. Ovarian cancer is reduced in women after tubal ligation.
The relationship between use of oral contraceptives and ovarian cancer was shown in a summary of results of 45 case-control and prospective studies. Cumulatively these studies show a protective effect for ovarian cancers. Women who used oral contraceptives for 10 years had about a 60% reduction in risk of ovarian cancer. (risk ratio .42 with statistical significant confidence intervals given the large study size, not unexpected). This means that if 250 women took oral contraceptives for 10 years, 1 ovarian cancer would be prevented. This is by far the largest epidemiological study to date on this subject (45 studies, over 20,000 women with ovarian cancer and about 80,000 controls).
The link to the use of fertility medication, such as Clomiphene citrate, has been controversial. An analysis in 1991 raised the possibility that use of drugs may increase the risk of ovarian cancer. Several cohort studies and case-control studies have been conducted since then without providing conclusive evidence for such a link. It will remain a complex topic to study as the infertile population differs in parity from the "normal" population.
There is good evidence that in some women genetic factors are important. Carriers of certain mutations of the BRCA1 or the BRCA2 gene. The BRCA1 and BRCA2 gene account for 5%-13% of ovarian cancers and certain populations (e.g. Ashkenazi Jewish women) are at a higher risk of both breast cancer and ovarian cancer, often at an earlier age than the general population. Patients with a personal history of breast cancer or a family history of breast and/or ovarian cancer, especially if at a young age, may have an elevated risk.
A strong family history of uterine cancer, colon cancer, or other gastrointestinal cancers may indicate the presence of a syndrome known as hereditary nonpolyposis colorectal cancer (HNPCC, also known as Lynch II syndrome), which confers a higher risk for developing ovarian cancer. Patients with strong genetic risk for ovarian cancer may consider the use of prophylactic i.e. preventative oophorectomy after completion of childbearing.
A Swedish study, which followed more than 61,000 women for 13 years, has found a significant link between milk consumption and ovarian cancer. According to the BBC, "[Researchers] found that milk had the strongest link with ovarian cancer - those women who drank two or more glasses a day were at double the risk of those who did not consume it at all, or only in small amounts." Recent studies have shown that women in sunnier countries have a lower rate of ovarian cancer, which may have some kind of connection with exposure to Vitamin D.
Other factors that have been investigated, such as talc use, asbestos exposure, high dietary fat content, and childhood mumps infection, are controversial and have not been definitively proven.
"Associations were also found between alcohol consumption and cancers of the ovary and prostate, but only for 50 g and 100 g a day."
Classification
Ovarian cancer is classified according to the histology of the tumor, obtained in a pathology report. Histology dictates many aspects of clinical treatment, management, and prognosis.
- Surface epithelial-stromal tumour, also known as ovarian epithelial carcinoma, is the most common type of ovarian cancer. It includes serous tumour, endometrioid tumor and mucinous cystadenocarcinoma.
- Sex cord-stromal tumor, including estrogen-producing granulosa cell tumor and virilizing Sertoli-Leydig cell tumor or arrhenoblastoma, accounts for 8% of ovarian cancers.
- Germ cell tumor accounts for approximately 30% of ovarian tumors but only 5% of ovarian cancers, because most germ cell tumors are teratomas and most teratomas are benign (see Teratoma). Germ cell tumor tends to occur in young women and girls. The prognosis depends on the specific histology of germ cell tumor, but overall is favorable.
- Mixed tumors, containing elements of more than one of the above classes of tumor histology.
Ovarian cancer can also be a secondary cancer, the result of metastasis from a primary cancer elsewhere in the body. Common primary cancers are breast cancer and gastrointestinal cancer (in which case the ovarian cancer is a Krukenberg cancer ). Surface epithelial-stromal tumor can originate in the peritoneum (the lining of the abdominal cavity), in which case the ovarian cancer is secondary to primary peritoneal cancer, but treatment is basically the same as for primary surface epithelial-stromal tumor involving the peritoneum.
Symptoms
Studies on the accuracy of symptoms
Two case-control studies, both subject to results being inflated by spectrum bias, have been reported. The first found that women with ovarian cancer had symptoms of increased abdominal size, bloating, urge to pass urine and pelvic pain. The smaller, second study found that women with ovarian cancer had pelvic/abdominal pain, increased abdominal size/bloating, and difficulty eating/feeling full. The latter study created a symptom index that was considered positive if any of the six (6) symptoms "occurred >12 times per month but were present for <1 year".They reported a sensitivity of 57% for early-stage disease and specificity 87% to 90%.
Ovarian Cancer Symptoms Consensus Statement
In 2007, the Gynecologic Cancer Foundation, Society of Gynecologic Oncologists and American Cancer Society originated the following consensus statement regarding the symptoms of ovarian cancer.
Ovarian cancer is called a “silent killer” because symptoms were not thought to develop until the disease had advanced and the chance of cure or remission poor. However, the following symptoms are much more likely to occur in women with ovarian cancer than women in the general population. These symptoms include:
- Bloating
- Pelvic or abdominal pain
- Difficulty eating or feeling full quickly
- Urinary symptoms (urgency or frequency)
- Pain during sex
Women with ovarian cancer report that symptoms are persistent and represent a change from normal for their bodies. The frequency and/or number of such symptoms are key factors in the diagnosis of ovarian cancer. Several studies show that even early stage ovarian cancer can produce these symptoms. Women who have these symptoms almost daily for more than a few weeks should see their doctor, preferably a gynecologist. Prompt medical evaluation may lead to detection at the earliest possible stage of the disease. Early stage diagnosis is associated with an improved prognosis.
Several other symptoms have been commonly reported by women with ovarian cancer. These symptoms include fatigue, indigestion, back pain, pain with intercourse, constipation and menstrual irregularities. However, these other symptoms are not as useful in identifying ovarian cancer because they are also found in equal frequency in women in the general population who do not have ovarian cancer.
Diagnosis
Ovarian cancer at its early stages(I/II) is difficult to diagnose until it spreads and advances to later stages (III/IV). This is due to the fact that most of the common symptoms are non-specific.
When an ovarian malignancy is included in the list of diagnostic possibilities, a limited number of laboratory tests are indicated. A complete blood count (CBC) and serum electrolyte test should be obtained in all patients.
The serum BHCG level should be measured in any female in whom pregnancy is a possibility. In addition, serum alpha-fetoprotein (AFP) and lactate dehydrogenase (LDH) should be measured in young girls and adolescents with suspected ovarian tumors because the younger the patient, the greater the likelihood of a malignant germ cell tumor.
A blood test called CA-125 is useful in differential diagnosis and in follow up of the disease, but it has not been shown to be an effective method to screen for early-stage ovarian cancer due to its unacceptable low sensitivity and specificity. However, this is the only available, widely-used marker currently.
Current research is looking at ways to combine tumor markers proteomics along with other indicators of disease (i.e. radiology and/or symptoms) to improve accuracy. The challenge in such an approach is that the very low population prevalence of ovarian cancer means that even testing with very high sensitivity and specificity will still lead to a number of false positive results (i.e. performing surgical procedures in which cancer is not found intra-operatively). However, the contributions of proteomics are still in the early stages and require further refining. Current studies on proteomics mark the beginning of a paradigm shift towards individually tailored therapy.
A pelvic examination and imaging including CT scan and trans-vaginal ultrasound are essential. Physical examination may reveal increased abdominal girth and/or ascites (fluid within the abdominal cavity). Pelvic examination may reveal an ovarian or abdominal mass. The pelvic examination can include a rectovaginal component for better palpation of the ovaries. For very young patients, magnetic resonance imaging may be preferred to rectal and vaginal examination.
To definitively diagnose ovarian cancer, a surgical procedure to take a look into the abdomen is required. This can be an open procedure (laparotomy, incision through the abdominal wall) or keyhole surgery (laparoscopy). During this procedure, suspicious areas will be removed and sent for microscopic analysis. Fluid from the abdominal cavity can also be analysed for cancerous cells. If there is cancer, this procedure can also determine its spread (which is a form of tumor staging).
Staging
Ovarian cancer staging is by the FIGO staging system and uses information obtained after surgery, which can include a total abdominal hysterectomy, removal of (usually) both ovaries and fallopian tubes, (usually) the omentum, and pelvic (peritoneal) washings for cytology. The AJCC stage is the same as the FIGO stage.
- Stage I - limited to one or both ovaries
- IA - involves one ovary; capsule intact; no tumor on ovarian surface; no malignant cells in ascites or peritoneal washings
- IB - involves both ovaries; capsule intact; no tumor on ovarian surface; negative washings
- IC - tumor limited to ovaries with any of the following: capsule ruptured, tumor on ovarian surface, positive washings
- Stage II - pelvic extension or implants
- IIA - extension or implants onto uterus or fallopian tube; negative washings
- IIB - extension or implants onto other pelvic structures; negative washings
- IIC - pelvic extension or implants with positive peritoneal washings
- Stage III - microscopic peritoneal implants outside of the pelvis; or limited to the pelvis with extension to the small bowel or omentum
- IIIA - microscopic peritoneal metastases beyond pelvis
- IIIB - macroscopic peritoneal metastases beyond pelvis less than 2 cm in size
- IIIC - peritoneal metastases beyond pelvis > 2 cm or lymph node metastases
- Stage IV - distant metastases to the liver or outside the peritoneal cavity
Para-aortic lymph node metastases are considered regional lymph nodes (Stage IIIC).
Treatment
Surgical treatment may be sufficient for malignant tumors that are well-differentiated and confined to the ovary. Addition of chemotherapy may be required for more aggressive tumors that are confined to the ovary. For patients with advanced disease a combination of surgical reduction with a combination chemotherapy regimen is standard. Borderline tumors, even following spread outside of the ovary, are managed well with surgery, and chemotherapy is not seen as useful.
Surgery is the preferred treatment and is frequently necessary to obtain a tissue specimen for differential diagnosis via its histology. Surgery performed by a specialist in gynecologic oncology usually results in an improved result. Improved survival is attributed to more accurate staging of the disease and a higher rate of aggressive surgical excision of tumor in the abdomen by gynecologic oncologists as opposed to general gynecologists and general surgeons.
The type of surgery depends upon how widespread the cancer is when diagnosed (the cancer stage), as well as the presumed type and grade of cancer. The surgeon may remove one (unilateral oophorectomy) or both ovaries (bilateral oophorectomy), the fallopian tubes (salpingectomy), and the uterus (hysterectomy). For some very early tumors (stage 1, low grade or low-risk disease), only the involved ovary and fallopian tube will be removed (called a "unilateral salpingo-oophorectomy," USO), especially in young females who wish to preserve their fertility.
In advanced malignancy, where complete resection is not feasible, as much tumor as possible is removed (debulking surgery). In cases where this type of surgery is successful (i.e. < 1 cm in diameter of tumor is left behind ["optimal debulking"]), the prognosis is improved compared to patients where large tumor masses (> 1 cm in diameter) are left behind. Minimally invasive surgical techniques may facilitate the safe removal of very large (greater than 10 cm) tumors with fewer complications of surgery.
Chemotherapy has been a general standard of care for ovarian cancer for decades, although with highly variable protocols.
Chemotherapy is used after surgery to treat any residual disease, if appropriate. This depends on the histology of the tumor; some kinds of tumor (particularly teratoma) are not sensitive to chemotherapy. In some cases, there may be reason to perform chemotherapy first, followed by surgery.
For patients with stage IIIC epithelial ovarian adenocarcinomas who have undergone successful optimal debulking, a recent clinical trial demonstrated that median survival time is significantly longer for patient receiving intraperitoneal (IP) chemotherapy.
Patients in this clinical trial reported less compliance with IP chemotherapy and fewer than half of the patients received all six cycles of IP chemotherapy. Despite this high "drop-out" rate, the group as a whole (including the patients that didn't complete IP chemotherapy treatment) survived longer on average than patients who received intravenous chemotherapy alone.
Some specialists believe the toxicities and other complications of IP chemotherapy will be unnecessary with improved IV chemotherapy drugs currently being developed.
Although IP chemotherapy has been recommended as a standard of care for the first-line treatment of ovarian cancer, the basis for this recommendation has been challenged.
Radiation therapy is not effective for advanced stages because when vital organs are in the radiation field, a high dose cannot be safely delivered.
Prognosis
Ovarian cancer usually has a poor prognosis. It is disproportionately deadly because it lacks any clear early detection or screening test, meaning that most cases are not diagnosed until they have reached advanced stages. More than 60% of patients presenting with this cancer already have stage III or stage IV cancer, when it has already spread beyond the ovaries. Ovarian cancers shed cells into the naturally occurring fluid within the abdominal cavity. These cells can implant on other abdominal (peritoneal) structures, included the uterus, urinary bladder, bowel and the lining of the bowel wall (omentum). These cells can begin forming new tumor growths before cancer is even suspected.
The five-year survival rate for all stages of ovarian cancer is 45.5%. For cases where a diagnosis is made early in the disease, when the cancer is still confined to the primary site, the five-year survival rate is 92.7%.
Germ cell tumors of the ovary have a much better prognosis than other ovarian cancers, in part because they tend to grow rapidly to a very large size, hence they are detected sooner.
Complications
- Spread of the cancer to other organs
- Progressive function loss of various organs
- Ascites (fluid in the abdomen)
- Intestinal obstructions
These cells can implant on other abdominal (peritoneal) structures, including the uterus, urinary bladder, bowel, lining of the bowel wall (omentum) and, less frequently, to the lungs.
Prevention
The use of oral contraceptives (birth control pills) for five years or more decreases the risk of ovarian cancer in later life by 50%.
Ovarian cancer in non-humans
Ovarian tumors have been reported in mares. Reported tumor types include teratoma, cystadenocarcinoma, and particularly granulosa cell tumor.
See also
External links
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