How breast cancer develops

Ductal breast cancer is thought to begin with a growth of cells in a breast duct. A. A typical breast duct is shown. B. An overgrowth of cells may develop in the breast duct. This is called hyperplasia. C. Over time, the cells develop changes that make them look different from typical cells. This is called atypical hyperplasia. D. The atypical cells may continue to build up. The cells are trapped in the breast duct. This is called ductal carcinoma in situ. E. Eventually the cancer cells may break out of the duct and become invasive breast cancer. The cells can spread to other parts of the body.