Very likely, breast/ovarian cancer risk and the responsiveness of BRCA-linked cancers to poly(ADP) ribose polymerase (PARP) inhibitors are reflections of HR functions shared by BRCA1 and BRCA2. The additional phenotypic “overlay” associated with BRCA1-linked cancers may reflect the impact of perturbing BRCA1 functions that are not shared with BRCA2. This evidence concerns the gene BRCA1 and cancer.