Breast cancers are not all alike. They can start in any tissue of the breast, and each type of breast cancer has distinct symptoms and prognosis.
Most types of breast cancer start in the ducts, but a smaller percentage start in the lobules and even fewer start in other tissues of the breast.
Breast cancers are named after their unique characteristics. For example, breast cancers that arise from epithelial cells are called carcinomas. Cancers arising from the stroma (supporting fibrous breast tissue) are called sarcomas.
Some types of breast cancer are named based on where the disease began, such as invasive ductal carcinoma. Others are named for their appearance under a microscope. For example, tubular carcinoma appears as tube-shaped cells under the microscope.
Invasive (or infiltrating) ductal carcinoma. This accounts for 70 percent of all breast cancers. It is the most common type of breast cancer. It begins inside the duct, then penetrates the duct's wall to reach the fatty tissue of the breast. From there, it has the potential to spread (or metastasize) to other parts of the body through the lymphatic system and bloodstream.
Invasive (or infiltrating) lobular carcinoma. This is the second-most common breast cancer. It accounts for 9 to 10 percent of all breast cancers. It begins in the terminal ducts of the milk-producing glands.
Medullary carcinoma. While these account for only 3 to 6 percent of all breast cancers, medullary carcinomas are more common in women with a genetic predisposition to breast cancer. In fact, studies have found that they account for 13 and 19 percent of all cancers in women who carry a BRCA1 mutation. In BRCA2 mutation carriers, 3 percent of the breast cancers are medullary carcinomas. In this type of cancer, the border between the cancer tissue and the normal tissues is relatively well-defined. Generally, the prognosis for women with medullary carcinoma is better than for women with other types of invasive ductal or lobular carcinoma.
Paget's disease. This unique cancer accounts for only 3 percent of all breast cancers. It involves the nipple and areola, and is often associated with abnormal scaling and redness of the skin in these areas. Women may also have burning or itching. Paget's disease may be associated with in situ or invasive cancer. If a biopsy shows there is no lump or evidence of ductal carcinoma in situ, the prognosis for this cancer is very good.
Inflammatory breast cancer accounts for approximately 1 percent of all breast cancers. It is named after its characteristic initial symptoms, which include redness, warmth, and swelling of the skin of the breast—often without a distinctive lump. These symptoms,have the appearance of an infection or inflammation but are caused by cancer cells blocking lymph vessels or channels in the skin over the breast.
Other rare forms of cancer and variants of invasive ductal carcinoma. Mucinous, or colloid, carcinoma accounts for 3 percent of breast cancers and is more common among older women. Tubular carcinoma and papillary carcinoma each represent around 1 percent of breast cancer diagnoses. Both mucinous and tubular carcinomas have a better prognosis than the more common type of invasive ductal or lobular breast cancer. Adenocystic breast cancer and carcinosarcoma breast cancer are even more rare form of cancers, accounting for 0.4 percent and 0.1 percent of all cases, respectively.
References:
American Cancer Society. (2004). Cancer Facts and Figures 2004. Atlanta, GA: American Cancer Society.
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Breast Cancer Linkage Consortium. (1997). Pathology of familial breast cancer: difference between breast cancers in carriers of BRCA1 or BRCA2 mutations and sporadic cases. Lancet 349(9064): 1505-1510.
Armes, J.E. et al. (1998).The histologic phenotypes of breast carcinoma occurring before age 40 years in women with and without BRCA1 or BRCA2 germline mutations: a population-based study. Cancer 83(11): 2335-2345.
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