Ovarian cancer is a type of cancer that originates in the ovaries. The female reproductive system contains two ovaries, one on each side of the uterus. Each ovary produces eggs as well as the hormones estrogen and progesterone. Ovarian cancer often goes undetected until it has spread within the pelvis and abdomen, which makes it more difficult to treat. Early-stage ovarian cancer, in which the disease is confined to the ovary, is more likely to be treated successfully.