Ovarian cancer is a type of cancer that begins in the ovaries. The ovaries — each about the size of an almond — produce eggs (ova) as well as the hormones estrogen and progesterone. The most common type of ovarian cancer is called ovarian epithelial cancer. It begins in the tissue that covers the ovaries. Cancer sometimes begins at the end of the fallopian tube near the ovary and spreads to the ovary. Cancer can also begin in the peritoneum and spread to the ovary. The stages and treatment are the same for ovarian epithelial, fallopian tube, and primary peritoneal cancers. Another type of ovarian cancer is ovarian germ cell tumor, which is much less common. It begins in the germ (egg) cells in the ovary.