Ovarian cancer begins in the cells that form the ovaries. Among these cells are surface epithelial cells, germ cells, and the sex cord-stromal cells. This is why cancer cells that metastasize from other organ sites to the ovary are not called ovarian cancer. Breast and colon cancers are examples of such cancers.

It has been observed that the majority of women with epithelial ovarian cancer are not diagnosed early enough. The diagnosis is done only when the disease has reached an advanced stage. By that time, the cancer spreads to the upper abdomen (stage I) or beyond (stage II). The chance of these women surviving five years is only 15 to 20 percent. But the chance of survival for the same period is 90% for patients in stage I, and about 70% for stage II patients.

Some ovarian tumors are benign, in which case the patient can be cured by surgically removing one ovary or the part of the ovary hosting the tumor. Some are malignant or cancerous. Malignant ovarian tumors are generally of three types: epithelial tumors, germ cell tumors and stromal tumors.

Epithelial tumors, accounting for most of the cases, develop in a layer of cube-shaped cells known as the germinal epithelium, which surrounds the outside of the ovaries. Its victims are mostly teenagers and young women. Germ cell tumors are not so common, and are found in the egg-maturation cells of the ovary. These patients can not only be cured, but also their fertility protected. Dangerous if allowed to spread, stromal tumors originate from connective tissue cells that hold the ovary together and produce the female hormones estrogen and progesterone.

All ovarian tumors are not cancerous. Benign cysts, dermoid tumors, and borderline malignant tumors all are distinct from ovarian cancer. These are curable and rarely prove fatal.