In the catchment area of the participating hospitals in our study, 102 known living female mutation carriers had undergone prophylactic mastectomy by Feb 2, 2015, when the study started (BRCA1, n = 67; BRCA2, n = 35), potentially preventing incident breast cancer in some mutation carriers during the period of time that the BRCAsearch study was open. Here, BRCA1 is linked to breast cancer.