BRCA1 and breast cancer: Of those who were older than 50 years of age at first breast cancer, 21.6% (95%CI, 12.3% to 30.8%) from families with a BRCA1 mutation, 15.5% (95% CI, 7.8% to 23.3%) from families with a BRCA2 mutation and 12.9% (95% CI 8.9% to 17.0%) from BRCA1/2 negative families developed contralateral breast cancer (Figure 3A, B, C).