(UroToday.com) Radium-223 is an alpha particle emitter that causes DNA double strand breaks and has been FDA-approved for use in mCRPC patients with bone metastases. PARP-1 activity critically supports androgen receptor activity in mCRPC and potentiates androgen receptor-dependent DNA damage response pathways that promote prostate cancer cell survival. Niraparib is a potent and selective PARP-1/2 inhibitor that has shown single-agent clinical activity in mCRPC. Dr. Eddy Yang and colleagues previously reported the safety of targeting the PARP-1/AR axis with niraparib in combination with radium-223 at ASCO 2020. At the 2021 American Society of Clinical Oncology (ASCO) Annual Meeting, Dr. Yang presented results of an exploratory biomarker analysis in the NiraRad phase Ib clinical trial.