The breakthrough in this area was the discovery that PARPi act as a potent therapeutic agent in cancers harbouring HR repair defects, such as those with BRCA mutations.[12, 88, 89, 90] The basis for this synthetic lethality is that in HR‐deficient cells, DSBs generated by PARP inhibition cannot be repaired leading to mitotic catastrophe and/or apoptosis. This evidence concerns the gene PARP1 and cancer.