PARP1 and cancer: Moreover, gene alterations, mutations, or functional loss of proteins involved in DDR mechanisms result in defective ATR, CHEK1, CHEK2, DSS1, MRE11A/NBS1, Fanconi anemia complementation group (FANC family of genes), EMSY, XRCC2, XRCC3, or PTEN, predispose patients to the success of PARP inhibitors for cancer treatment [165,166,167,168].