There are examples for such differences: BRCA1 and BRCA2 carrier-specific modifiers, such as the recently identified variant at 6p24, which was associated with breast cancer risk only in BRCA2 carriers [6], and the ovarian cancer susceptibility locus 4q32, which appeared to modify ovarian cancer risk only for BRCA1 carriers [7]. This evidence concerns the gene BRCA1 and breast cancer.