The 25-year cumulative risk of contralateral breast cancer after first breast cancer was 44.1% (95%CI, 37.6% to 50.6%) for relatives from families with a BRCA1 mutation, 33.5% (95%CI, 22.4% to 44.7%) for relatives from families with a BRCA2 mutation and 17.2% (95%CI, 14.5% to 19.9%) for relatives from families without a BRCA1/2 mutation. Here, BRCA1 is linked to breast cancer.