The Impact of Uncommon HRR Alterations as Predictors of Efficacy of PARP Inhibitors in Metastatic Castration-Resistant Prostate Cancer: A Meta-Analysis of Randomized Controlled Trials

Background: Metastatic castration-resistant prostate cancer (mCRPC) patients with BRCA1/2 mutations show significant responses to poly-ADP ribose polymerase inhibitors (PARPi), while the efficacy of these agents in patients with homologous recombination repair (HRR) gene alterations other than BRCA remains unclear. Objective: This meta-analysis aimed at assessing the efficacy of PARPi in mCRPC harboring alterations in four rare HRR genes (i.e. CDK12, PALB2, ATM, and CHEK2). Patients and methods: Five randomised phase III trials (PROfound, PROpel, MAGNITUDE, TALAPRO-2, TRITON3) were selected through searching the Medline/PubMed, Cochrane Library, and ASCO Meeting abstracts. Data extraction followed the PRISMA statement. The primary endpoints, radiographic progression-free survival (rPFS) and overall survival (OS) with the relative 95% CI, were calculated using fixed- or random-effects methods, depending on the studies’ heterogeneity. RevMan software for meta-analysis (v.5.2.3) was used. Results: PARPi significantly improved rPFS in mCRPC patients with CDK12 alterations (hazard ratio (HR) = 0.65; p = 0.02) without OS benefit. In patients with ATM, CHEK2, or PALB2 alterations, no significant benefit was observed in rPFS or OS. Due to the low incidence of these rare mutations, we grouped them into gene panels, revealing a significant rPFS advantage when CDK12+PALB2 (HR = 0.63; p = 0.009) were combined, and a similar benefit when including CHEK2 in the gene panel (HR = 0.69; p = 0.01). Conclusion: CDK12 alterations could be considered as a predictive biomarker of rPFS benefit with PARPi. A gene panel grouping CDK12 and PALB2 with or without CHEK2 mutations could also enable prediction of rPFS benefit with PARPi.