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 is thought to most commonly form in the outer lining of the ovary (resulting in epithelial ovarian cancer) and, less commonly, 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 called "the silent killer" because it frequently causes non-specific symptoms, which contribute to diagnostic delay, resulting 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).

An abnormal physical examination (including a pelvic examination), a blood test (for CA-125, more specifically) or medical imaging studies can provide evidence leading to an ovarian cancer diagnosis. 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. Older women, and in those who have a first or second degree relative with the disease, have an increased risk. 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. Fact: date=November 2007 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.