The following is provided by the National Cancer Institute

Ovarian cancer is one of the most challenging of all cancers to fight, because it often goes undiagnosed until it is advanced.

There are several different types of ovarian cancer. The most common type is epithelial carcinoma that grows on the outer surface of the ovary. Two more rare, types of ovarian cancer include germ-cell tumors, which begin in the egg-producing cells of a woman’s ovaries, and stromal tumors, which originate in the supportive tissue around the ovaries.

Cancer cells from all three types of ovarian cancer may also spread to the bloodstream via the lymphatic system and travel to other areas of the body. This process of spreading is referred to as metastasis.

According to the Ovarian Cancer National Alliance, ovarian cancer occurs in about one out of every 69 women. More than 20,000 women are diagnosed with ovarian cancer each year.

While the exact causes of ovarian cancer are not yet known, there is a noted genetic predisposition. For example, a woman with a first-degree relative (mother, sister or daughter) who has been diagnosed with ovarian cancer is at higher risk than one who does not—particularly if more than one such relative has been diagnosed. Also, women with a family history of cancer of the breast, uterus, colon or rectum may also have an increased risk of ovarian cancer.

Most women are over age 55 when diagnosed with ovarian cancer. Older women who have never been pregnant have an increased risk of ovarian cancer. Some studies have suggested that women who take estrogen by itself (estrogen without progesterone) for 10 or more years may have an increased risk of ovarian cancer.

Scientists have also studied whether taking certain fertility drugs, using talcum powder, or being obese are risk factors. It is not clear whether these are risk factors, but if they are, they are not strong risk factors.

Having a risk factor does not mean that a woman will get ovarian cancer. Most women who have risk factors do not get ovarian cancer. On the other hand, women who do get the disease often have no known risk factors, except for growing older.