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).
Female breasts are also known as mammary glands because they are able to produce milk.
Noninvasive Breast Cancer
Noninvasive breast cancers include:
- Ductal carcinoma in situ (DCIS; also called intraductal carcinoma). 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. DCIS is the most common type of noninvasive breast cancer.
- Lobular carcinoma in situ (LCIS). Although it is technically not a cancer, lobular carcinoma in situ is a marker for an increased risk of invasive breast cancer.
A diagnosis of these early cancers (DCIS and LCIS) is made when 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:
Click the icon to see an image of the breast.
- Invasive (also called infiltrating) ductal carcinoma. This type of invasive breast cancer penetrates the wall of a milk-passage duct. It comprises between 70 - 80% of all breast cancer cases.
- Invasive (also called infiltrating) lobular carcinoma. This is invasive cancer that has spread through the wall of a milk-producing lobule. It accounts for 10 - 15% of all breast cancers. It may sometimes appear in both breasts, sometimes in several separate locations.
There are other less common breast cancers that are not discussed in this report.