BRCA1 and breast cancer: An effect was not observed in BRCA2 carriers, but BRCA1 carriers whose age at menarche was 14–15 years had a 54% reduction in breast cancer risk compared to those with menarche at ⩽11 years of age (OR=0.46, 95% CI 0.30–0.69) (Kotsopoulos et al, 2005).