PARP1 and neoplasm: Given PARP1 and PARP2 are both targets for inhibitors being used to treat tumours with defects in homologous recombination (HR)22,23, unravelling these complexities will be important not only for understanding the mechanistic basis of DNA repair, but also refining the use of PARP inhibitors (PARPi) in the clinic and guiding the development of novel PARPi with new mechanisms of action.