Objective: To evaluate the rate of prophylactic contralateral mastectomy in an international cohort of women with hereditary breast cancer and to evaluate the predictors of uptake of preventive surgery.

Methods: Women with a BRCA1 or BRCA2 mutation who had been diagnosed with unilateral breast cancer were followed prospectively for a minimum of 1.5 years. Information was collected on prophylactic surgery, tamoxifen use, and the occurrence of contralateral breast cancer.

Results: Nine hundred twenty-seven women were included in the study; of these, 253 women (27.3%) underwent a contralateral prophylactic mastectomy after the initial diagnosis of breast cancer. There were large differences in uptake of contralateral prophylactic mastectomy by country, ranging from 0% in Norway to 49.3% in the United States. Among women from North America, those who had a prophylactic contralateral mastectomy were significantly younger at breast cancer diagnosis (mean age, 39 years) than were those without preventive surgery (mean age, 43 years). Women who initially underwent breast-conserving surgery were less likely to undergo contralateral prophylactic mastectomy than were women who underwent a mastectomy (12% v 40%; P < 10(-4)). Women who had elected for a prophylactic bilateral oophorectomy were more likely to have had their contralateral breast removed than those with intact ovaries (33% v 18%; P < 10(-4)).

Conclusions: Age, type of initial breast cancer surgery, and prophylactic oophorectomy are all predictive of prophylactic contralateral mastectomy in women with breast cancer and a BRCA mutation. The acceptance of contralateral preventive mastectomy was much higher in North America than in Europe.