First, for Nigerian women, BRCA1 and BRCA2 have a major effect on breast cancer incidence both because the ORs for BRCA1 and BRCA2 are extremely high (> 20 for BRCA1; > 10 for BRCA2) and because 11% of patients carry a damaging mutation in one of these genes (7.0% in BRCA1; 4.1% in BRCA2). This evidence concerns the gene BRCA1 and breast cancer.