Recently, it has become apparent that germline mutations in genes that are part of the homologous recombination machinery are not only associated with the development of breast cancer and various human cancers but may also influence the sensitivity of breast cancers to therapy because defects in the homologous recombination pathway are associated with hypersensitivity to PARP inhibitors and other chemotherapeutic agents [30,31]. This evidence concerns the gene PARP1 and cancer.