A mastectomy is when a whole breast is removed as treatment for breast cancer. In the case of a simple mastectomy one or more lymph nodes will also be removed to check that the cancer has not spread. In a radical mastectomy all the lymph nodes on the affected side will be removed. In some cases women are given a double mastectomy – either because both breasts are affected or else in order to prevent the possibility of further cancers in the other breast.