Breast Cancer Types

Most breast cancers are carcinomas—malignant tumors that grow out of epithelial (surface or lining) tissues. Less than 1 percent of breast cancers are sarcomas—tumors arising from connective tissue, bone, muscle, or fat.

In addition, the most common type of breast cancer (about 75 percent of cases) is ductal carcinoma, which develops in the tissues that line the milk ducts. A much smaller number of cancers (about 7 percent) 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 some controversy over whether to treat DCIS by some form of breast-sparing surgery, with or without radiation, or by mastectomy.

Unfortunately, breast cancers often grow through the base membrane that surrounds the lobules or ducts. These cancers are termed infiltrating or invasive carcinomas. Roughly 95 percent of all breast cancers are invasive.

Invasive breast cancers—such as ductal or lobular carcinomas—can gain access to supporting tissue between the ducts (called stroma), 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.

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). Individuals may develop one, the other, or a combination of invasive and noninvasive breast cancers. If a patient has both types of cancer, treatment is based on the stage of the invasive component.

Breast Cancer Subtypes

In many cases, the cell type does not affect the type or duration of therapy that a patient receives. However, according to a report issued by the American Cancer Society (ACS), the U.S. Centers for Disease Control and Prevention (CDC), the U.S. National Cancer Institute (NCI), and the North American Association of Central Cancer Registries in March 2015, classifying breast cancers according to four tumor subtypes could help improve treatment.

This report states that breast cancers differ on a molecular level according to the following:

  • Hormone receptor (HR) status—how a chemical receptor on the cancer cell reacts to hormones like estrogen
  • Cancer cell activity around the HER2 gene

The four breast cancer subtypes are:

  1. Luminal A (HR+/HER2–)
  2. Luminal B (HR+/HER2+)
  3. HER2-enriched (HR–/HER2+)
  4. Triple negative (HR–/HER2–)

Each breast cancer subtype responds differently to treatment and has a different survival rate, according to the Journal of the National Cancer Institute. Recording these breast cancer subtypes in national cancer registries will help researchers rank breast cancer risk more accurately and lead to better treatments for individual patients.

Updated by Remedy Health Media

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 14 Aug 1999

Last Modified: 02 Sep 2015