Ovarian cancer is a cancerous tumor of an ovary. It may originate from the ovary itself or more commonly from communicating nearby structures such as fallopian tubes or the inner lining of the abdomen. The ovary is made up of three different cell types including epithelial cells, germ cells, and stromal cells. When these cells become abnormal, they have the ability to divide and form tumors. These cells can also invade or spread to other parts of the body. When this process begins, there may be no or only vague symptoms. Symptoms become more noticeable as the cancer progresses. These symptoms may include bloating, vaginal bleeding, pelvic pain, abdominal swelling, constipation, and loss of appetite, among others. Common areas to which the cancer may spread include the lining of the abdomen, lymph nodes, lungs, and liver.

The risk of ovarian cancer increases with age. Most cases of ovarian cancer develop after menopause. It is also more common in women who have ovulated more over their lifetime. This includes those who have never had children, those who began ovulation at a younger age and those who reach menopause at an older age. Other risk factors include hormone therapy after menopause, fertility medication, and obesity. Factors that decrease risk include hormonal birth control, tubal ligation, pregnancy, and breast feeding. About 10% of cases are related to inherited genetic risk; women with mutations in the genes BRCA1 or BRCA2 have about a 50% chance of developing the disease. Some family cancer syndromes such as hereditary nonpolyposis colon cancer and Peutz-Jeghers syndrome also increase the risk of developing ovarian cancer. Epithelial ovarian carcinoma is the most common type of ovarian cancer, comprising more than 95% of cases. There are five main subtypes of ovarian carcinoma, of which high-grade serous carcinoma (HGSC) is the most common. Less common types of ovarian cancer include germ cell tumors and sex cord stromal tumors. A diagnosis of ovarian cancer is confirmed through a biopsy of tissue, usually removed during surgery.

Screening is not recommended in women who are at average risk, as evidence does not support a reduction in death and the high rate of false positive tests may lead to unneeded surgery, which is accompanied by its own risks. Those at very high risk may have their ovaries removed as a preventive measure. If caught and treated in an early stage, ovarian cancer is often curable. Treatment usually includes some combination of surgery, radiation therapy, and chemotherapy. Outcomes depend on the extent of the disease, the subtype of cancer present, and other medical conditions. The overall five-year survival rate in the United States is 49%. Outcomes are worse in the developing world.

In 2020, new cases occurred in approximately 313,000 women. In 2019 it resulted in 13,445 deaths in the United States. Death from ovarian cancer increased globally between 1990 and 2017 by 84.2%. Ovarian cancer is the second-most common gynecologic cancer in the United States. It causes more deaths than any other cancer of the female reproductive system. Among women it ranks fifth in cancer-related deaths. The typical age of diagnosis is 63. Death from ovarian cancer is more common in North America and Europe than in Africa and Asia. In the United States, it is more common in White and Hispanic women than Black or American Indian women.

Early signs and symptoms of ovarian cancer may be absent or subtle. In most cases, symptoms exist for several months before being recognized and diagnosed. Symptoms can often be misdiagnosed as irritable bowel syndrome. The early stages of ovarian cancer tend to be painless which makes it difficult to detect it early on. Symptoms can vary based on the subtype. Ovarian borderline tumors, also known as low malignant potential (LMP) ovarian tumors, do not cause an increase in CA125 levels and are not identifiable with an ultrasound. The typical symptoms of an LMP tumor can include abdominal distension or pelvic pain. Particularly large masses tend to be benign or borderline.

The most typical symptoms of ovarian cancer include bloating, abdominal or pelvic pain or discomfort, back pain, irregular menstruation or postmenopausal vaginal bleeding, pain or bleeding after or during sexual intercourse, loss of appetite, fatigue, diarrhea, indigestion, heartburn, constipation, nausea, feeling full, and possibly urinary symptoms (including frequent urination and urgent urination).

Later symptoms of ovarian cancer are due to the growing mass causing pain by pressing on other abdominopelvic organs or from metastases. Because of the anatomic location of the ovaries deep in the pelvis, most masses are large and advanced at the time of diagnosis. The growing mass may cause pain if ovarian torsion develops. If these symptoms start to occur more often or more severely than usual, especially after no significant history of such symptoms, ovarian cancer is considered. Metastases may cause a Sister Mary Joseph nodule. Rarely, teratomas can cause growing teratoma syndrome or peritoneal gliomatosis. Some experience menometrorrhagia and abnormal vaginal bleeding after menopause in most cases. Other common symptoms include hirsutism, abdominal pain, virilization, and an adnexal mass.

In adolescents or children with ovarian tumors, symptoms can include severe abdominal pain, irritation of the peritoneum, or bleeding. Sex cord stromal tumors produce hormones which can lead to the premature development of secondary sex characteristics. Sex cord-stromal tumors in prepubertal children may be manifested by signs of early puberty; abdominal pain and distension are also common. Adolescents with sex cord-stromal tumors may experience amenorrhea. As the cancer becomes more advanced, it can cause an accumulation of fluid in the abdomen and lead to distension. If the malignancy has not been diagnosed by the time it causes ascites, it is typically diagnosed shortly thereafter. Advanced cancers can also cause abdominal masses, lymph node masses, or pleural effusion.