Ovarian cancer starts in the ovaries. There are two ovaries, one on each side of the uterus in the pelvis. The ovaries produce eggs that travel through the fallopian tubes into the uterus, where the fertilized egg implants and develops into a fetus. The ovaries are the main source of the female hormones estrogen and progesterone.
The ovaries consist of three kinds of cells where tumors can develop: germ cells, which form eggs; stromal cells, which release hormones and connect the structures of the ovaries; and epithelial cells, which cover the outer surface of the ovaries (most ovarian tumors are epithelial cell tumors). Some tumors are non-cancerous and never spread beyond the ovary. Benign tumors can be treated either by removing the ovary or the portion of the ovary that contains the tumor. However, malignant (cancerous) or low malignant potential ovarian tumors can spread to other parts of the body and could be fatal.