Breast cancer is a disease in which cancer cells grow in the breast tissue.
Cancer occurs when cells in the body divide without control or order. If cells keep dividing uncontrollably, a mass of tissue forms. This is called a growth or tumor. The term cancer refers to malignant tumors. They can invade nearby tissue and spread to other parts of the body.
Although most people think of breast cancer as affecting women, men can develop breast cancer as well. Breast cancer in men can be more aggressive.