Direct evidence for such genetic modifiers of risk has been obtained through the association studies performed by the Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA), which have shown that several common breast cancer susceptibility alleles identified through population-based genome-wide association studies (GWASs) are also associated with breast cancer risk among BRCA1 and BRCA2 mutation carriers [8–10]. This evidence concerns the gene BRCA1 and breast cancer.