LBA50Pre-specified interim analysis of GALAHAD: A phase II study of niraparib in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and biallelic DNA-repair gene defects (DRD)

Abstract Background Effective therapies for pts with treatment-refractory mCRPC are an important unmet medical need. Niraparib is a highly selective poly ADP-ribose polymerase (PARP) inhibitor of PARP-1 and PARP-2 DNA-repair polymerases. Methods GALAHAD is an ongoing open-label phase II study assessing niraparib (300 mg daily) in pts with mCRPC and DRD with disease progression on taxane and androgen receptor-targeted therapy. DRD status was evaluated by a plasma or tissue-based test and defined as having biallelic alterations in BRCA1/2 (BRCA), ATM, FANCA, PALB2, CHEK2, BRIP1, or HDAC2. Primary endpoint was objective response rate (ORR) by RECIST 1.1 with no evidence of bone progression as per the PCWG3 criteria. Composite response rate (CRR) was defined as ORR, conversion of circulating tumor cells to