Human cancers with underlying defects in HDR (such as BRCA1 inactivated breast and ovarian cancers) (Bryant et al., 2005; Farmer et al., 2005; Audeh et al., 2010; Tutt et al., 2010) show sensitivity to poly (ADP-ribose) polymerase 1 (PARP) inhibition. The gene discussed is PARP1; the disease is ovarian carcinoma.