There are several different types of ovarian cancer, which are classified according to the type of cell from which they start.

Epithelial ovarian carcinoma [EOC]

This is the most common type of ovarian cancer, which arises from the cells covering the surface of the ovaries [epithelial cells]. This type accounts for 65-90% of ovarian cancer cases. Epithelial ovarian carcinomas include the following types:

Grade of ovarian cancer

Epithelial carcinomas are further divided into grades according to how the degree of differentiation, or maturity, of the cells making up the tumor. Well-differentiated tumors have a better prognosis than poorly differentiated tumors. Clear cell and undifferentiated carcinoma have a poorer prognosis than the other cell types.

Germ cell carcinoma

This type of ovarian cancer arises from the cells that form the eggs and makes up about 5 percent of ovarian cancer cases. While germ cell carcinoma can occur in women of any age, it tends to be found most often in women in their earlier 20s. There are six main types of germ cell carcinoma, but the three most common types are: Teratomas, Dysgerminomas and Endodermal sinus tumors. There are also many tumors that arise in the germ cells that are benign.

Stromal carcinoma

Ovarian stromal carcinoma accounts for the remaining 5 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 with epithelial ovarian carcinoma, 70 percent of the cases of stromal carcinoma are diagnosed in Stage I.