Located in the pelvis, one on each side of the uterus, the ovaries (each about the size of a walnut) are the part of a woman's reproductive system. They make the female hormones, estrogen and progesterone, and they produce eggs (ova). The eggs travel through the fallopian tubes into the uterus (womb) where the fertilized egg implants itself and grows into a fetus.  After menopause, the ovaries make smaller amounts of the hormones and stop producing eggs.

The ovaries contain three kinds of cells:

• Epithelial cells cover the ovaries.
• Germ cells produce eggs inside the ovaries.
• Stromal cells make most of the estrogen and progesterone.

Cancer is a disease of the cells. Cells normally grow in an orderly fashion.  But when they grow uncontrollably, they can form a mass of abnormal or cancerous cells. 

Most (about 85 to 90%) of ovarian cancers start in the epithelial cells. A cancerous growth of cells may be limited to one place.  Or the cancer can spread, invading and destroying the cells of other organs and body parts. This is called "metastatic cancer."  Metastasize means to spread; cancer that has "metastasized" has spread to other parts of the body.  For example, if ovarian cancer cells invade the liver, the disease in the liver is not called "liver cancer," but "metastasized ovarian cancer."  The more aggressive the cancer, the further and faster it spreads. 

Many paradoxes surround ovarian cancer.  Early detection is one of the best defenses against its worst effects, but it's one of the hardest cancers to detect early.  That's why it's one of the deadliest gynecological cancers; it caused more than 15,000 deaths in the U.S. in 2006.  Yet it's also relatively rare; only about 3% of cancers among women are ovarian. In contrast, lung cancer causes about 25% of female cancer deaths.

One of the most complete sources of information about ovarian cancer is the American Cancer Society's Detailed Guide which you can download from their website.