ovarian cancer : Understanding Ovarian Cancer

Cancer is a group of many related diseases that begin in cells, the body's basic unit of life. To understand cancer, it is helpful to know about normal cells and what happens when they become cancerous.

The body is made up of many types of cells. Normally, cells grow, divide, and produce more cells when the body needs them. This orderly process helps to keep the body healthy. Sometimes, however, cells keep dividing when new cells are not needed. These extra cells form a mass of tissue, called a growth or tumor. Tumors can be benign or malignant.

Benign tumors are not cancer. They often can be removed and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body. Most important, benign tumors are rarely a threat to life.

Ovarian cysts are a different type of growth. They are fluid-filled sacs that form on the surface of an ovary. They are not cancer. Cysts often go away without treatment. If a cyst does not go away, the doctor may suggest removing it, especially if it seems to be growing.


Malignant tumors are cancer. Cells in these tumors are abnormal and divide without control or order. They can invade and damage nearby tissues and organs. Cancer cells can also spread (metastasize) from their original site to other parts of the body.

A malignant tumor that begins in the ovaries is called ovarian cancer. There are several types of ovarian cancer. Ovarian cancer that begins on the surface of the ovary (epithelial carcinoma) is the most common type. This is the type of cancer discussed in this booklet. Ovarian cancer that begins in the egg-producing cells (germ cell tumors) and cancer that begins in the supportive tissue surrounding the ovaries (stromal tumors) are rare and are not discussed in this booklet. The Cancer Information Service and the other NCI sources listed under "National Cancer Institute Information Resources" can provide information or suggest resources that deal with these types of ovarian cancer.

Ovarian cancer cells can break away from the ovary and spread to other tissues and organs in a process called shedding. When ovarian cancer sheds, it tends to seed (form new tumors) on the peritoneum (the large membrane that lines the abdomen) and on the diaphragm (the thin muscle that separates the chest from the abdomen). Fluid may collect in the abdomen. This condition is known as ascites. It may make a woman feel bloated, or her abdomen may look swollen.

Ovarian cancer cells can also enter the bloodstream or lymphatic system (the tissues and organs that produce and store cells that fight infection and disease). Once in the bloodstream or lymphatic system, the cancer cells can travel and form new tumors in other parts of the body.

A Service of the National Cancer Institute