Ovarian cancer begins in the ovaries, the reproductive glands on each side of the uterus that produce eggs and hormones. Ovarian cancer often goes undetected until it has spread within the pelvis and abdomen. At this late stage, ovarian cancer is more difficult to treat and is frequently fatal. Early-stage ovarian cancer, in which the disease is confined to the ovary, is more likely to be treated successfully.
The ovaries are made of three main kinds of cells. Each can develop into a different type of tumor:
- Epithelial tumors, which begin in the thin layer of tissue that covers the outside of the ovaries. About 90 percent of ovarian cancers are epithelial tumors.
- Stromal tumors, which begin in the ovarian tissue that contains hormone-producing cells. These tumors are usually diagnosed at an earlier stage than other ovarian tumors. About 7 percent of ovarian tumors are stromal.
- Germ cell tumors, which begin in the egg-producing cells. These rare ovarian cancers tend to occur in younger women.