Breast Cancer Types
Most breast cancers are carcinomasthat is, they are malignant tumors that grow out of epithelial (surface or lining) tissues. Less than 1% of breast cancers are sarcomas, or tumors arising from connective tissue, bone, muscle, or fat.
In addition, the most common type of breast cancer (about 75% of cases) is ductal carcinoma, which develops in the tissues that line the milk ducts (see also Breast Anatomy). A much smaller number of cancers (about 7%) are found within the breast lobules and are called lobular carcinomas. Paget's disease (cancer of the areola and nipple) and inflammatory carcinoma account for nearly all other forms of breast cancer.
There are two major groups of breast cancer:
- Noninvasive carcinoma
- Invasive carcinoma
If cancer cells do not penetrate surrounding tissues and stay within the confines of a duct or lobule, they are called noninvasive, in situ tumors (tumors that remain "in the site" of origin). In situ carcinomas are too small to have formed a "lump" and usually cannot be felt during a physical exam. They are discovered by mammography. Noninvasive carcinomas include lobular carcinoma in situ (LCIS) and ductal carcinoma in situ (DCIS). DCIS also is considered a potential marker for the development of invasive carcinoma. There is considerable controversy over whether to treat DCIS by some form of breast-sparing surgery, with or without radiation, or by mastectomy (see also Treatment of Breast Cancer).
Unfortunately, breast cancers often grow through the basement membrane that surrounds the lobules or ducts. These cancers are termed infiltrating or invasive carcinomas. Roughly 95% of all breast cancers are invasive.
Invasive breast cancers such as ductal or lobular carcinomascan gain access to the stroma (supporting tissue) between the ducts, blood vessels, lymphatic vessels, and nerves. Thus, there is a greater chance that cancer will spread throughout the body. Invasive carcinomas may be composed of several different cell types.
Some rare, invasive breast cancers include tubular cancers (slow-growing, tube-shaped cancers), medullary cancers (cancers that look like the gray matter of the brain), and mucinous cancers (cancers containing mucus proteins). Yet, for the most part, the cell type does not affect the type or duration of therapy that a patient receives.
Individuals may develop one, the other, or a combination of invasive and noninvasive breast cancer. If a patient has both types of cancer, treatment is based on the stage of the invasive component.