This enhanced dependence on certain DDR components—sometimes via the concept of synthetic lethality, where loss of one cellular pathway leads to reliance on an alternative pathway—came into the spotlight with the development of poly-(ADP-ribose) polymerase (PARP) inhibitors as precision medicines for certain cancers harboring defects in the DDR mechanism of homologous recombination (Lord and Ashworth 2017). Here, PARP1 is linked to cancer.