Breast Cancer - Metaplastic: Overview

Approved by the Cancer.Net Editorial Board, 08/2014

ON THIS PAGE: You will find some basic information about this disease and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Metaplastic Breast Cancer. To see other pages, use the menu on the side of your screen. Think of that menu as a roadmap to this full guide.

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 change and grow uncontrollably, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can spread to other parts of the body. A benign tumor means the tumor will not spread.

About the breast

The breast is mainly made up 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, which is the 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 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 different from the much more common ductal or lobular breast cancer. Most often, metaplastic breast cancer starts in the epithelial cells, and then changes into squamous or nonglandular cells. Also, metaplastic breast cancer does not have estrogen receptors (ERs), progesterone receptors (PRs), or the HER2 receptor, which is a protein found in ductal and lobular breast cancers. When a breast cancer does not have these receptors it is called triple-negative breast cancer or TNBC. Metaplastic breast cancer is considered a subtype of triple-negative breast cancer.

Metaplastic breast cancer can spread to the lymph nodes and other parts of the body, especially the lungs. When it is first diagnosed, metaplastic breast cancer is considered an invasive cancer, meaning that it has already spread beyond the duct or lobe.

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