A preventive mastectomy or prophylactic mastectomy or risk-reducing mastectomy (RRM) is an elective operation to remove the breasts so that the risk of breast cancer is reduced.

The procedure is a surgical option for individuals who are at high risk for the development of breast cancer. High risk women without a prior history of personal breast cancer might consider bilateral risk-reducing mastectomy (BRRM) as an option for minimising the risk of primary breast carcinoma development. The procedure includes the surgical removal of both breasts before any pathologic diagnosis has been made. Women that were previously diagnosed with a breast cancer in one breast (ipsilateral breast cancer) might elect to undergo risk-reducing mastectomy of the other unaffected (contralateral) breast, that is to say contralateral risk-reducing mastectomy (CRRM), to minimize the risk of a second breast cancer development. CRRM has been shown to reduce the incidence of contralateral breast cancer, but there is not sufficient evidence that it improves survival. Women who had a bilateral mastectomy in 2013 were about 10 years younger than those who had a unilateral mastectomy.

This preventive operation pertains to women with these characteristics:

Discussions and decision should be made with the help of specialists who can use relevant information and statistical models to predict the individual lifetime risk of development of breast cancer.

Undergoing a preventive mastectomy does not guarantee that breast cancer will not develop later, however, it reduces the risk by 90% in high risk women. Also, a preventive mastectomy may not be able to remove all breast tissue as some of it may be in the arm pit, near the collar bone, or in the abdominal wall.

Male carriers of BRCA1 and BRCA2 mutations have a higher risk of breast cancer than other males, approximately 1.2% and 6.8%, but their risk is much lower than in female mutation carriers (about 60%) and lower than in the general female population (12%). Thus, preventive mastectomy has not been advocated for affected men.

In most situations the operation involves both breasts and thus represents a bilateral procedure. When cancer has affected already one breast, the other breast, still healthy, may be removed in a unilateral preventive mastectomy. Typically either a simple, a subcutaneous or a nipple-sparing mastectomy is performed. With the former the areola and nipple are removed, while the other two approaches preserve the nipple area for cosmetic reasons. To increase the viability of the nipple area for preservation during mastectomy, a so-called "nipple delay" procedure can be done several weeks before the mastectomy. Reconstructive breast surgery can be performed in the same surgical setting, added after the mastectomy. Saline or silicone implants may be used in the reshaping process and may be placed in a later setting.

A preventive mastectomy carries certain risks including those of anesthesia, bleeding, infection, pain, disfiguration, anxiety and disappointment.