How much does prophylactic mastectomy reduce the risk of breast cancer?

Prophylactic mastectomy can reduce the chances of developing breast cancer in women at high risk of the disease:

• For women with the BRCA1 or BRCA2 mutation, prophylactic mastectomy reduces the risk of developing breast cancer by 90 to 95 percent.
• For women who have already had breast cancer and also have a family history of the disease, prophylactic mastectomy can reduce the risk of developing cancer in the other breast by 90 to 95 percent.

However, studies indicate that prophylactic mastectomy of the unaffected breast (contralateral prophylactic mastectomy) has little or no effect on overall survival for women who have had breast cancer in one breast and do not have genetic mutations or hereditary risk factors.

Having a prophylactic mastectomy doesn't guarantee that you'll never develop breast cancer because all of your breast tissue can't be removed during the surgery. Sometimes breast tissue can be found in your chest, armpit or skin, above your collarbone, or on the upper part of your abdominal wall.

It is impossible for a surgeon to remove all of this breast tissue. Although the chances are slim, breast tissue remaining in your body can still develop breast cancer.