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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.

5571 Background: In the Phase III PAOLA-1/ENGOT-ov25 trial, the addition of maintenance olaparib (ola) to bevacizumab (bev) in patients (pts) with newly diagnosed advanced high-grade ovarian cancer (HGOC) resulted in prolonged progression-free survival (PFS), particularly for pts with HRD-positive tumors including a BRCA1/ BRCA2 mutation (BRCAm; Ray-Coquard et al. NEJM 2019). Preclinical data suggest that pts with mutations (mut) in the RING domain of BRCA1 are less sensitive to ola. The magnitude of benefit from ola + bev, according to the location of mut in the functional domains (FD) of BRCA , remains to be explored. Methods: Pts with newly diagnosed advanced HGOC in response after platinum-based chemotherapy + bev received maintenance bev (15 mg/kg q3w for 15 months [mo]) + either ola (300 mg bid for 24 mo) or placebo (pbo). In this post hoc exploratory analysis, PFS was analyzed in pts with BRCAm according to mut location in the FDs of BRCA1 (RING, DNA-binding domain [DNA-BD], or BRCA1 C terminus [BRCT]) and BRCA2 (RAD51-BD; DNA-BD). Results: Among the 806 randomized pts, 235 (29.2%) harbored a BRCAm: 160 (19.9%) with a BRCA1 mut and 76 (9.4%) with a BRCA2 mut. BRCA1 mut in FDs of RING, DNA-BD and BRCT were detected in 19 (11.8%), 41 (25.6%) and 34 (21.2%) pts, respectively. BRCA2 mut were detected in FDs of RAD51-BD and DNA-BD in 37 (48.7%) and 14 (18.4%) pts, respectively. With a median follow-up of 25.5 mo, 24-mo PFS rates and hazard ratios (HRs) according to mut locations are reported in the Table. In pts with a BRCA1 DNA-BD mut, 24-mo PFS was 89% and 14% (ola + bev vs pbo + bev; HR 0.08, 95% confidence interval [CI] 0.02–0.26) compared with 64% and 24% for pts with mut in RING + BRCT + other domains (HR 0.33, 95% CI 0.19–0.57). In pts with BRCA2 mut, 24-mo PFS for pts with mut in the DNA-BD was 91% vs 100% (ola + bev vs pbo + bev) compared with 82% and 44% for pts with mut in RAD51-BD + other domains (HR 0.21, 95% CI 0.08–0.54). Conclusions: In this exploratory analysis, pts with newly diagnosed advanced HGOC and a BRCAm had a PFS benefit from maintenance ola + bev regardless of mut locations in BRCA1/BRCA2. Sensitivity to ola + bev maintenance was particularly high for pts with mut in the DNA-BD of BRCA1. Pts with a mut in the DNA-BD of BRCA2 commonly had excellent outcomes. Clinical trial information: NCT02477644. [Table: see text]