First, after your mammogram results come back, your doctor will determine the course of treatment if a malignancy is found. Typically, if the tumor is small enough, it will be removed without removing all of the breast tissue. However, if the tumor has spread to all tissues, a mastectomy will be performed. A mastectomy is the removal of breast tissue. Nowadays, thanks to advances in cancer research and treatment, this procedure can be avoided through early protection. However, when most women hear that cancer is a possibility for them, they undergo a mastectomy, when in reality, only 25% of people with the breast cancer gene actually develop breast cancer..