Homologous Recombination Repair Gene Mutations to Predict Olaparib Plus Bevacizumab Efficacy in the First-Line Ovarian Cancer PAOLA-1/ENGOT-ov25 Trial

Abstract

PURPOSE The PAOLA-1/ENGOT-ov25 trial of maintenance olaparib plus bevacizumab for newly diagnosed advanced high-grade ovarian cancer demonstrated a significant progression-free survival (PFS) benefit over placebo plus bevacizumab, particularly in patients with homologous recombination deficiency (HRD)–positive tumors. We explored whether mutations in non- BRCA1 or BRCA2 homologous recombination repair (non–BRCA HRRm) genes predicted benefit from olaparib plus bevacizumab in PAOLA-1. METHODS Eight hundred and six patients were randomly assigned (2:1). Tumors were analyzed using the Myriad MyChoice HRD Plus assay to assess non–BRCA HRRm and HRD status; HRD was based on a genomic instability score (GIS) of ≥ 42. In this exploratory analysis, PFS was assessed in patients harboring deleterious mutations using six non–BRCA HRR gene panels, three devised for this analysis and three previously published. RESULTS The non–BRCA HRRm prevalence ranged from 30 of 806 (3.7%) to 79 of 806 (9.8%) depending on the gene panel used, whereas 152 of 806 (18.9%) had non‐ BRCA1 or BRCA2 mutation HRD-positive tumors. The majority of tumors harboring non–BRCA HRRm had a low median GIS; however, a GIS of > 42 was observed for tumors with mutations in five HRR genes ( BLM, BRIP1, RAD51C, PALB2, and RAD51D). Rates of gene-specific biallelic loss were variable (0% to 100%) in non–BRCA HRRm tumors relative to BRCA1-mutated (99%) or BRCA2-mutated (86%) tumors. Across all gene panels tested, hazard ratios for PFS (95% CI) ranged from 0.92 (0.51 to 1.73) to 1.83 (0.76 to 5.43). CONCLUSION Acknowledging limitations of small subgroup sizes, non–BRCA HRRm gene panels were not predictive of PFS benefit with maintenance olaparib plus bevacizumab versus placebo plus bevacizumab in PAOLA-1, irrespective of the gene panel tested. Current gene panels exploring HRRm should not be considered a substitute for HRD determined by BRCA mutation status and genomic instability testing in first-line high-grade ovarian cancer.