(UroToday.com) Inhibitors of poly (ADP-ribose) polymerase or PARP enzymes are under development in many contexts within oncology. These drugs are thought to be efficacious in the context of impaired DNA damage repair (DDR), especially deficiencies in homologous recombination repair, by further inhibiting PARP-mediated DNA repair mechanisms and thus resulting in tumor cell death. Based on a recent randomized clinical trial, the PARP inhibitor olaparib was recently approved by the United States Federal Drug Administration (FDA) for treatment of metastatic castration-resistant prostate cancer (mCRPC) for patients with suspected deleterious somatic or germline alterations in genes involved in homologous recombination repair. Other PARP inhibitors in development include talazoparib (which has the highest in vitro PARP trapping effect), rucaparib, niraparib, and veliparib.