5595 Background: DUO-E (NCT04269200) showed statistically significant, clinically meaningful improvement in progression-free survival (PFS) with addition of durvalumab to CP, followed by durvalumab ± the PARP inhibitor olaparib, vs CP alone for patients (pts) with EC (Westin SN et al. J Clin Oncol 2024;42:283–99). PARP inhibitors are an established approach to targeting tumors with homologous recombination deficiency, so we performed post hoc exploratory analyses of PFS by BRCAm status. Methods: Pts with newly diagnosed FIGO Stage III/IV or recurrent EC and naïve to first-line systemic treatment were randomized 1:1:1 to CP (CP + durvalumab placebo [pbo; 6 cycles] followed by durvalumab pbo + olaparib pbo), CP+D (CP + durvalumab [1120 mg q3w; 6 cycles] followed by durvalumab [1500 mg q4w] + olaparib pbo) or CP+D+O (CP + durvalumab [6 cycles] followed by durvalumab + olaparib [300 mg bid]). Tissue BRCAm status was determined retrospectively (FoundationOneCDx assay, Foundation Medicine). Results: Of 718 pts randomized, 19.9% were mismatch repair deficient (dMMR) and 80.1% MMR proficient (pMMR). At primary analysis (April 12, 2023), PFS improvement was observed for CP+D and CP+D+O vs CP irrespective of BRCAm status (Table). BRCAm prevalence was low overall (dMMR: 12.6% BRCAm, 61.5% non-BRCAm, 25.9% unknown; pMMR: 4.0% BRCAm, 65.9% non-BRCAm, 30.1% unknown). PFS outcomes for CP+D+O vs CP in pMMR non-BRCAm pts (HR 0.57, 95% CI 0.42–0.78) were consistent with the overall pMMR subgroup (HR 0.57, 95% CI 0.44–0.73); BRCAm subgroup analyses were descriptive due to small sample size. Conclusions: Clinical benefit with addition of durvalumab to CP, followed by durvalumab + olaparib, vs CP alone was observed in the ITT and pMMR populations irrespective of BRCAm status. Clinical trial information: NCT04269200 . [Table: see text]