Different types of ovarian cancer are classified according to the type of cell from which they start.

Epithelial tumors

About 90 percent of ovarian cancers develop in the epithelium, the thin layer of tissue that covers the ovaries. This form of ovarian cancer generally occurs in postmenopausal women.

Germ cell carcinoma tumors

Making up about five percent of ovarian cancer cases, this type begins in the cells that form eggs. While germ cell carcinoma can occur in women of any age, it tends to be found most often in women in their early 20s. Six main kinds of germ cell carcinoma exist, but the three most common types are: teratomas, dysgerminomas and endodermal sinus tumors.

Many tumors that arise in the germ cells are benign.

Stromal carcinoma tumors

Ovarian stromal carcinoma accounts for about five percent of ovarian cancer cases. It develops in the connective tissue cells that hold the ovary together and those that produce the female hormones estrogen and progesterone. The two most common types are granulosa cell tumors and sertoli-leydig cell tumors. Unlike epithelial ovarian carcinoma, 70 percent of stromal carcinoma cases are diagnosed in Stage I.

Small cell carcinoma of the ovary

Small cell carcinoma of the ovary (SCCO) is a rare, highly malignant tumor that affects mainly young women, with a median age at diagnosis of 24 years old. The subtypes of SCCO include pulmonary, neuro-endocrine and hypercalcemic. SCCO accounts for 0.1 percent of ovarian cancer cases. Approximately two-thirds of patients with SCCO have hypercalcemia. The symptoms are the same as other types of ovarian cancer.

For more specific information about the different types of ovarian cancer, see the American Cancer Society’s detailed guide.

Keep reading for more information about the stages of ovarian cancer.