Types of Breast Cancer

Ninety percent of breast cancer are adenocarcinomas, which arise from glandular tissue. Within this broad category, there is a great degree of variation. For instance, there are about 30 different subtypes of adenocarcinoma.

The earliest form of the disease, ductal carcinoma in situ, comprises about 15-20% of all breast cancers and develops solely in the milk ducts. The most common type of breast cancer, invasive ductal carcinoma, develops from ductal carcinoma in situ, spreads through the duct walls, and invades the breast tissue.

Cancer that begins in the lobes or lobules is called lobular (small cell) carcinoma and is more likely to be found in both breasts. Invasive lobular carcinoma originates in the milk glands and accounts for 10-15% of invasive breast cancers. Both ductal and lobular carcinomas can be either in situ, or self-contained; or infiltrating, meaning penetrating the wall of the duct or lobe and spreading to adjacent tissue.

Less common types of breast cancer include the following:

• Inflammatory breast cancer (diffuse brawny infiltration; breast appears red or inflamed; tends to spread quickly)
• Medullary carcinoma (originates in central breast tissue)
• Mucinous carcinoma (invasive; usually occurs in postmenopausal women)
• Paget disease of the nipple (originates in the milk ducts and spreads to the skin of the nipples or areola)
• Phyllodes tumor (tumor with a leaf-like appearance that extends into the ducts; rarely metastasizes)
• Tubular carcinoma (small tumor that is often undetectable by palpation)

Sarcomas (cancer of the connective tissue) and lymphomas (cancer of the lymph tissue) rarely develop in the breasts.