(UroToday.com) Since 2015, multiple studies together have suggested that approximately a quarter of metastatic castration-resistant prostate cancer (mCRPC) tumors have mutations in DNA damage repair (DDR) genes. These alterations, especially those in genes for homologous recombination repair (HRR), are associated to varying degrees with response to PARP inhibitor therapy. Two PARP inhibitors are now approved for the care of patients with mCRPC and mutations in certain HRR genes: olaparib (based on PROfound trial) and rucaparib (based on TRITON2 trial). Given the significance of alterations in HRR genes in mCRPC, genomic testing for HRR alterations has been included in mCRPC treatment guidelines with the purpose of guiding genetic counseling and therapy selection.