PARP1 and neoplasm: Olaparib, a first-in-class oral poly(ADP-ribose) polymerase (PARP) inhibitor, functions by trapping PARP1 and PARP2 on DNA at sites of single-strand breaks, thereby preventing DNA repair and leading to synthetic lethality in tumor cells deficient in homologous recombination repair—such as those with BRCA1/2 mutations.