Breast Cancer:

What Is Breast Cancer?

Breast cancer is a malignant tumor that starts from cells of the breast. A malignant tumor is a group of cancer cells that may invade surrounding tissues or spread (metastasize) to distant areas of the body. The disease occurs almost entirely in women, but men can get it, too. The remainder of this document refers only to breast cancer in women. For information on breast cancer in men, see the American Cancer Society's document, Breast Cancer in Men.

Normal Breast Structure

In order to understand breast cancer, it is helpful to have some basic knowledge about the normal structure of the breasts.
 

The female breast is made up mainly of lobules (milk-producing glands), ducts (tiny tubes that carry the milk from the lobules to the nipple), and stroma (fatty tissue and connective tissue surrounding the ducts and lobules, blood vessels, and lymphatic vessels).

Most breast cancers begin in the cells that line the ducts (ductal cancers); some begin in the cells that line the lobules (lobular cancers), and the rest in other tissues.

For more information, visit http://www.breastcancer.org/