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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 forms in the lining of the ovary (resulting in epithelial ovarian cancer)[1] or in the egg cells (resulting in a germ cell tumor). 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).[2]
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.[3] 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.[4][5][6] 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.[7]
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).[8][9]
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.[citation needed] 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.[citation needed]
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).[10]
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. [11] It will remain a complex topic to study as the infertile population differs in parity from the “normal” population.
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