Breast tissue consists of 15-20 independent sections, each of which opens into the nipple with a separate duct. Between these parts are muscle and support tissues, fat, nerves, blood and lymph vessels. Each of these milk ducts opens vertically to the nipple separately.

Breast cancer is a tumoral formation consisting of cells in the milk glands of the breast and among the cells lining the ducts that carry the milk produced to the nipple, which proliferate uncontrollably as a result of various factors and have the potential to spread to other organs.

It is not known for certain which factors cause breast cancer. However, clinical studies have identified some factors that show a high probability. In some women, genetic predisposing gene mutations (disorders in the genes that predispose to cancer) increase the risk of breast cancer, while in other women the risk factor is being a woman herself.

Breast tissue, especially the nipple, is very rich in sensory nerves. Most of the lymphatic pathways of the breast go to the lymph nodes in the armpit and a very small number go to the lymph nodes in the chest cavity. A good understanding of the lymph nodes and lymph flow in the breast is also important for understanding the spread (metastasis) of breast cancer. Removal or sampling of the axillary lymph nodes is very important in the surgical treatment of breast cancer.

Breast cancer can develop from the milk glands or ducts of the breast.