© 2005-2012 American Society of Clinical Oncology (ASCO). All rights reserved worldwide.
Metaplastic breast cancer, also called metaplastic carcinoma of the breast, is a rare type of breast cancer. Cancer begins when normal cells in the breast begin to change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).
About the breast
The breast is mainly composed of fatty tissue. Within this tissue is a network of lobes, which are made up of tiny, tube-like structures called lobules that contain milk glands. Tiny ducts connect the glands, lobules, and lobes, carrying the milk from the lobes to the nipple, located in the middle of the areola (darker area that surrounds the nipple of the breast). Blood and lymph vessels run throughout the breast; blood nourishes the cells, and the lymph system drains bodily waste products. The lymph vessels connect to lymph nodes, the tiny, bean-shaped organs that ordinarily help fight infection.
About metaplastic breast cancer
Metaplastic breast cancer describes a cancer that begins in one type of cell (such as those from the glands of the breast) and changes into another type of cell. It is very different from the typical ductal or lobular breast cancer. Most cases of metaplastic breast cancer start in the epithelial cells, and then change into squamous (nonglandular) cells. Because the cells that give rise to metaplastic breast cancer are not part of the normal breast gland, this cancer does not have estrogen receptors (ERs), progesterone receptors (PRs), or HER2 (a protein found in 20% of ductal and lobular breast cancers).
Metaplastic breast cancer can spread to the lymph nodes and other areas of the body, especially the lungs. At the time of diagnosis, metaplastic breast cancer is considered an invasive cancer, meaning that it has already spread beyond the duct or lobe.
Find out more about basic cancer terms used in this section.