Efficacy of bilateral prophylactic mastectomy in women with a family history of breast cancer

Background Options for women at high risk for breast cancer include surveil lance, chemoprevention, and prophylactic mastectomy. The data on the outcom es for surveillance and prophylactic mastectomy are incomplete. Methods We conducted a retrospective study of all women with a family histo ry of breast cancer who underwent bilateral prophylactic mastectomy at the Mayo Clinic between 1960 and 1993. The women were divided into two groups - high risk and moderate risk - on the basis of family history. A control st udy of the sisters of the high-risk probands and the Gall model were used t o predict the number of breast cancers expected in these two groups in the absence of prophylactic mastectomy. Results We identified 639 women with a family history of breast cancer who had undergone bilateral prophylactic mastectomy: 214 at high risk and 425 a t moderate risk. The median length of follow-up was 14 years. The median ag e at prophylactic mastectomy was 42 years. According to the Gall model, 37. 4 breast cancers were expected in the moderate-risk group; 4 breast cancers occurred (reduction in risk, 89.5 percent; P<0.001). We compared the numbe rs of breast cancers among the 214 high-risk probands with the numbers amon g their 403 sisters who had not undergone prophylactic mastectomy. Of these sisters, 38.7 percent (156) had been given a diagnosis of breast cancer (1 15 cases were diagnosed before the respective proband's prophylactic mastec tomy, 38 were diagnosed afterward, and the time of the diagnosis was unknow n in 3 cases). By contrast, breast cancer was diagnosed in 1.4 percent (3 o f 214) of the probands. Thus, prophylactic mastectomy was associated with a reduction in the incidence of breast cancer of at least 90 percent. Conclusions In women with a high risk of breast cancer on the basis of fami ly history, prophylactic mastectomy can significantly reduce the incidence of breast cancer. (N Engl J Med 1999;340:77-84.) (C) 1999, Massachusetts Me dical Society.