The Breast Structure

The main parts of the female breast are lobules (milk producing glands), ducts (milk passages that connect the lobules and the nipple), and stroma (fatty tissue and ligaments surround­ing the ducts and lobules, blood vessels, and lymphatic vessels).

Most breast cancer begins in the ducts (ductal), some in the lobules (lobular), and the rest in other breast tissues. Lymph is a clear fluid that has tissue waste products and immune system cells. Most lymphatic vessels of the breast lead to under­arm (axillary) lymph nodes.

Some lead to lymph nodes above the collarbone (called supraclavicular) and others to internal mam­mary nodes which are next to the breastbone (or sternum). Cancer cells may enter lymph vessels and spread along these vessels to reach lymph nodes.

Cancer cells may also enter blood vessels and spread through the bloodstream and other parts of the body.

If breast cancer cells have spread to the axillary lymph nodes, it makes it more likely that they have spread to other organs of the body as well.