Originating in the ovaries, ovarian cancer has three main types of ovarian cancer tumors: epithelial tumors, germ cell tumors and stromal tumors. Most ovarian tumors are epithelial tumors that start in the cells that cover outer part of ovaries. According to Cancer.org, ovarian cancer accounts for about 3% of cancers among women, but it causes more deaths than any other cancer of the female reproductive system.