BRCA1 and cancer: Direct evidence for genetic modifiers of risk has been provided through studies that investigated the associations between common breast and ovarian cancer susceptibility variants, identified through genome-wide association studies (GWAS) or candidate gene studies in the general population, and cancer risk for BRCA1 and BRCA2 mutation carriers [3-8] and through GWAS in BRCA1 and BRCA2 mutation carriers [9-11].