PARP1 and cancer: Therefore the first well‐appreciated function of PARP1 is to mediate DNA damage response and repair.[49] Indeed, PARP1‐deficient cells and mice are more sensitive than wild‐type counterparts to genotoxic agents.[50] Seminal studies in 2005[51] demonstrated a specific lethality of homologous recombination‐deficient cancer cells upon PARP1 inhibition, paving the way to exploiting its DNA repair function for clinical cancer therapy.[3] The anti‐cancer effect of PARP1 inhibition supports PARP1‐mediated signaling as an endogenous protective mechanism in response to DNA damage.