A mastectomy is the surgical removal of the breast. It is used to treat breast cancer.

• Partial or segmental mastectomy is the removal of the area of the breast that contains cancer, some of the breast tissue around the tumor, and the lining over the chest muscles below the tumor. The lymph nodes under the arm are also removed and examined under a microscope (axillary lymph node dissection or sentinel node biopsy).
• Total (or simple) mastectomy is the removal of the whole breast.
• Modified radical mastectomy is the removal of the breast, the lymph nodes under the arm, the lining over the chest muscles, and sometimes part of the chest wall muscles.
• Radical mastectomy (Halsted radical mastectomy) is the removal of the breast, chest muscles, and all of the lymph nodes under the arm. For many years, this was the most common operation for breast cancer, but now it is rarely used.

The removal of the breast before cancer is diagnosed is called a prophylactic mastectomy. This type of mastectomy can be used to prevent breast cancer in women who have an extremely high risk of developing the disease.