Ovarian cancer is not a single disease. More than thirty different carcinomas can affect the ovaries. The World Health Organization (WHO) classifies ovarian tumors based on their cell type: epithelial, germ cell, stromal, and metastatic.

Epithelial tumors are the most commonly diagnosed ovarian cancers. They are abnormal masses that usually develop on the surface of the ovaries. Malignant epithelial growths are often diagnosed only when the disease is well advanced. Seventy-five percent of all epithelial cancers are diagnosed at Stage III or Stage IV. Epithelial tumors are further sub-divided by cell type.

Forty percent of epithelial tumors are serous growths. Serous cells produce a thin, watery fluid. Serous growths may be benign (serous cystadenoma), or malignant (serous cystadenocarcinoma). Fifty percent of such growths are malignant. Women between the ages of forty and sixty are most likely to develop serous tumors.

Epithelial tumors of endometrioid origin comprise approximately twenty percent of all cases. Eight percent are malignant, and most commonly affect women between the ages of fifty and seventy.

Twenty percent of ovarian endometrioid growths are associated with endometrial cancer, which develops on the cells lining the uterus. Five percent of cases have been linked to the presence of endometriosis: the growth of the uterine lining outside the uterus. The ovaries are a common location for endometriosis.

Mucinous cells produce a thick fluid called mucus. Cancers developing from ovarian mucinous cells are rare, comprising only one percent of epithelial tumors. However, when a mucinous carcinoma does develop, the growth is malignant eighty percent of the time. Mucinous growths are most common among women from thirty to sixty years of age.

Six percent of epithelial ovarian cancers are clear cell carcinomas. Almost all are malignant, and forty percent of cases have been linked to endometriosis. Women between the ages of forty and eighty are most at risk of clear cell carcinoma.

Borderline ovarian cancers may be composed of serous, clear cell, endometrioid or mucinous material, but spread slowly and have a high cure rate. Ten to fifteen percent of epithelial cases are borderline, and they develop most often between the ages of thirty and eighty. In most cases, surgical removal is enough to cure a borderline growth.

Brenner tumors are rare epithelial growths, present in only two to five percent of cases. They are usually benign.

Germ cell tumors arise in the germ cells, cells in the ovaries that have the potential to develop into eggs. They may also be called dermoid, or teratoma tumors. Benign "mature" teratomas are common ovarian cysts and may develop at any time after puberty.

Malignant ovarian teratomas account for only three to five percent of ovarian cancers. Sixty to seventy percent of the time, malignant teratomas are diagnosed at Stage I or Stage II, making them easier to treat than epithelial cancers.

The various types of malignant ovarian teratomas include:

Immature teratoma often develop in young women, often before the age of eighteen. The growths are labeled "immature" because they contain cells similar to those in a developing fetus. Immature teratoma have a high cure rate, even if the disease is diagnosed at an advanced stage.

Stromal sex-cord tumors are rare malignancies that generally appear before the age of fifty. Such growths tend to produce virilism: the development of male secondary sex characteristics. Symptoms may include:

Five percent of malignant ovarian tumors are cancers that spread to the ovaries from the breasts or gastrointestinal tract. For example, Krukenberg tumors are stomach cancers that have metastasized to the ovaries. Krukenberg malignancies often affect both ovaries.

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