BRCA1 and breast cancer: The previous study by Kuchenbaecker et al. [19] on contralateral breast cancer showed a 20-year cumulative risk after breast cancer diagnosis in 40% of BRCA1 carriers and 26% of BRCA2 carriers (hazard ratio for comparing BRCA2 vs BRCA1, 0.62; 95% CI 0.47–0.82; P = 0.001).