Healthy Breasts

To understand breast cancer, it helps to know something about the normal structure or parts of the breasts, as shown in the picture below.

A woman's breast is made up of glands that make breast milk (called lobules), ducts (small tubes that carry milk from the lobules to the nipple), fatty and connective tissue, blood vessels, and lymph (pronounced limf) vessels. Most breast cancers begin in the cells that line the ducts (ductal cancer), some begin in the lobules (lobular cancer), and a small number start in other tissues

BREAST LUMPS THAT ARE NOT CANCER

Most breast lumps are benign (not cancerous).  Benign breast tumors are abnormal growths, but they do not spread outside of the breast and they are not life threatening. But some benign breast lumps can increase a woman's risk of getting breast cancer.

Most lumps are caused by fibrocystic changes. Cysts are fluid-filled sacs. Fibrosis is the formation of scar-like tissue. These changes can cause breast swelling and pain. They often happen just before a woman's period is about to start. The breasts may feel lumpy, and sometimes there is a clear or slightly cloudy nipple discharge. For more on fibrocystic changes and other benign breast changes, please see our document, Non-cancerous Breast Conditions.

THE LYMPH SYSTEM

The lymph system is one of the main ways in which breast cancers can spread. Lymph nodes are small, bean-shaped groups of immune system cells (cells that fight infections) that are connected by lymphatic vessels. Lymphatic vessels are like small veins, except that they carry a clear fluid called lymph (instead of blood) away from the breast. Breast cancer cells can enter lymphatic vessels and begin to grow in lymph nodes.

Most lymph vessels of the breast lead to lymph nodes under the arm. These are called axillary nodes. If breast cancer cells reach the underarm lymph nodes and keep on growing, they cause the nodes to swell. The doctor needs to know whether cancer cells have spread to lymph nodes because if they have, there is a higher chance that the cells have also gotten into the bloodstream and spread to other places in the body. The more lymph nodes that have cancer in them, the more likely it is that the cancer will be found in other organs, too. This could affect the treatment plan.

Adapted from The American Cancer Society http://www.cancer.org/Cancer/BreastCancer/OverviewGuide/breast-cancer-overview-what-is-breast-cancer

Diagram from: http://www.oncolink.org/types/article.cfm?c=3&s=5&ss=838&id=9588

Last Medical Review: August 2010