Breast cancer is a type of cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas. While the overwhelming majority of cases are women, men can sometimes also develop breast cancer. Worldwide, breast cancer comprises 22.9% of all cancers in women.