Mammary Epithelial Cell Function and Abnormalities

The term mammary relates to the breasts, specifically, the milk glands in the breast. The word mammal is derived from the word mammary and is used to indicate animals that feed their young via maternal milk glands (cows have mammary glands in their udders.)

In other words, the female mammary glands are the breasts. Other words using mammary define structures found within the mammary glands or breasts. For example, the term mammary duct ectasia would refer to a process occurring in the breast duct, in this case, a dilated and blocked milk duct.

Human mammary epithelial cells

Definition of Epithelial Cells

Epithelial cells are defined as cells or tissue of the epithelium — a thin layer of tissue that covers or lines the surface of tubes or cavities within the body. When epithelial cells become malignant (become cancerous) they form tumors that are referred to as carcinomas. Around 80% of cancers in the human body are carcinomas.

Putting It Together

Putting the definitions together, mammary epithelial cells are cells in the thin layer of tissue that coat and lines the surface of the milk ducts in the breast. There are many ducts within each lobule that converge in the 15 to 20 lobes of the breast on their way to the tip of the nipple. There are specialized types of these mammary epithelial cells. Myoepithelial and luminal epithelial cells are two that occur in the milk ducts (see illustration).


In the picture, you can see how mammary epithelial cells line the milk ducts. The problem arises when these cells become "immortal" and grow without stopping. The first step of the cancerous transformation is called ductal carcinoma in situ of the breast (or DCIS,) a condition in which the cancer is limited to the inside of the duct and has not spread to surrounding tissues. At this point, the cells have not spread beyond the basement membrane and are considered "pre-cancerous."

DCIS does not always progress to cancer, but unfortunately, it happens too often.

When these abnormal cells break through the basement membrane — and invades or infiltrate other tissue — the condition is then known as invasive intraductal breast cancer — the most common type of breast cancer.

Pronunciation: e-pu-THEE-lee-al

Also Known As: Mammary epithelial cells, breast epithelial cells

Examples: Mammary epithelial cells line the ducts and lobes of your breast, and these cells produce breast milk. Most cases of breast cancer originate in epithelial cells.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Cancer Institute. Cancer Classification. SEER Training.

  2. National Cancer Institute. Breast Anatomy. Breast Anatomy. SEER Training.

  3. American Cancer Society. Ductal Carcinoma in Situ (DCIS).

Additional Reading
  • Dimri, G., Band, H., and V. Band. Mammary epithelial cell transformation: insights from cell culture and mouse models. Breast Cancer Research. 2005. 7:171-179.
  • National Cancer Institute. SEER Training Modules. Breast Anatomy. Accessed 01/27/16.

By Pam Stephan
Pam Stephan is a breast cancer survivor.