PARP1 and cancer: Studies in the past have shown that PARP inhibition sensitizes cells to ionizing radiation and DNA damaging genotoxic agents irrespective of HR status (Bernges and Zeller, 1996; Trucco et al., 1998; Menissier de Murcia et al., 2003) and the activity of PARP1/2 in cancer cells is critical in the establishment of resistance to genotoxic radio- and chemotherapies (Sarkaria et al., 2008; Michels et al., 2013).