Breast cancers are potentially life-threatening malignancies that develop in one or both breasts. The structure of the female breast is important in understanding this cancer:

The interior of the female breast consists mostly of fatty and fibrous connective tissues.
It is divided into about 20 sections called lobes.
Each lobe is further subdivided into a collection of lobules, structures that contain small milk-producing glands.
These glands secrete milk into a complex system of tiny ducts. The ducts carry the milk through the breast and converge in a collecting chamber located just below the nipple.
Breast cancer is either noninvasive (referred to as in situ, confined to the site of origin) or invasive (spreading).

The female breast is either of two mammary glands (organs of milk secretion) on the chest.

Noninvasive Breast Cancer

Noninvasive breast cancers include:

Ductal carcinoma in situ (also called intraductal carcinoma or DCIS). DCIS consist of cancer cells in the lining of the duct. DCIS is a non-invasive, early cancer, but if left untreated, it may sometimes progress to an invasive, infiltrating ductal breast cancer.
Lobular carcinoma in situ, or LCIS. Although noninvasive, lobular carcinoma in situ is a marker for an increased risk of invasive cancer in both breasts. (Some experts prefer to call this condition lobular neoplasia rather than refer to it as a cancer.) According to a 2001 report, for patients with LCIS the risk for developing invasive cancer in the same breast is about 18% -- and 14% in the other breast -- after 20 years. These invasive cancers can be either lobular or ductal.

At the time of diagnosis of these early cancers (DCIS and LCIS), there is no evidence of invasion.

Invasive Breast Cancer

Invasive cancer occurs when cancer cells spread beyond the basement membrane, which covers the underlying connective tissue in the breast. This tissue is rich in blood vessels and lymphatic channels that are capable of carrying cancer cells beyond the breast. Invasive breast cancers include the following:

Infiltrating ductal carcinoma. This is invasive breast cancer that penetrates the wall of a duct. It comprises between 70 - 80% of all breast cancer cases.
Infiltrating lobular carcinoma. This invasive cancer has spread through the wall of a lobule. It accounts for 10 - 15% of all breast cancers. It may sometimes appear in both breasts, sometimes in several separate locations.

Click the icon to see an image of the breast.

There are other less common breast cancers that are not discussed in this report.

Review Date: 10/2/2006
Reviewed By: Harvey Simon, M.D., Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.