Breast cancer is the tumorous growth of breast cells. It usually starts in the inner lining of milk ducts (Ductal Carcinoma) or in the lobules that supply them with milk (Lobular Carcinoma). The cells grow abnormally and divide at a much higher rate than the normal healthy cells. Such cells accumulate and form a lump or mass. They may also spread to the lymph nodes and other parts of the body.