New data from an exploratory analysis of the phase 3 DUO-E trial demonstrates that adding olaparib maintenance therapy to durvalumab plus chemotherapy significantly improves progression-free survival (PFS) across multiple biomarker and histological subgroups of patients with mismatch repair-proficient (pMMR) endometrial cancer. These findings were presented at the 2025 Society of Gynecologic Oncology Annual Meeting on Women's Cancer.
The analysis revealed consistent PFS benefits regardless of PD-L1 expression, POLE and TP53 mutation status, homologous recombination repair (HRR) mutation status, BRCA mutation status, histological type, and baseline circulating tumor DNA (ctDNA) levels.
"The benefit of adding olaparib to durvalumab in this population isn't driven by one particular subset benefiting. It seems to be distributed across the biomarkers, at least as we have tested them," explained lead study author Dr. Kathleen N. Moore, Virginia Kerley Cade Endowed Chair of Cancer Development and associate director of Clinical Research at the Stephenson Cancer Center.
Significant Risk Reductions Across Subgroups
The most substantial reductions in progression or death risk with the olaparib-durvalumab-chemotherapy combination versus chemotherapy alone were observed in:
- Patients with detectable ctDNA at baseline (HR, 0.36; 95% CI, 0.23-0.56)
- Those with positive PD-L1 expression (HR, 0.44; 95% CI, 0.31-0.61)
- Patients with serous disease histology (HR, 0.46; 95% CI, 0.27-0.76)
Even in the durvalumab-chemotherapy arm without olaparib, notable benefits were seen in patients with HRR-mutated disease (HR, 0.45; 95% CI, 0.23-0.87) and those with detectable ctDNA at baseline (HR, 0.61; 95% CI, 0.41-0.88) compared to chemotherapy alone.
DUO-E Trial Design and Primary Findings
The double-blind phase 3 DUO-E trial enrolled 718 patients with newly diagnosed stage III or IV recurrent endometrial cancer. Participants were randomized 1:1:1 to receive:
- Chemotherapy alone followed by placebo maintenance
- Chemotherapy plus durvalumab followed by durvalumab maintenance
- Chemotherapy plus durvalumab followed by maintenance with durvalumab and olaparib
The trial's primary endpoint was PFS per investigator assessment using RECIST criteria, with secondary endpoints including overall survival and safety.
In the intent-to-treat (ITT) population, median PFS was 9.6 months (95% CI, 9.0-9.9) with chemotherapy alone, 10.2 months (95% CI, 9.7-14.7) with durvalumab plus chemotherapy, and 15.1 months (95% CI, 12.6-20.7) with olaparib added to durvalumab and chemotherapy.
Both experimental arms met the trial's primary endpoint, with PFS improvements versus chemotherapy alone in the durvalumab arm (HR, 0.71; 95% CI, 0.57-0.89; P = .003) and the durvalumab/olaparib arm (HR, 0.55; 95% CI, 0.43-0.69; P <.0001).
Biomarker Analysis in pMMR Subpopulation
The pMMR biomarker subgroup analysis included 575 evaluable patients with known biomarker status. The subgroup showed high heterogeneity with frequent biomarker overlap:
- 100% had known histology at diagnosis
- 98% had known PD-L1 status
- 86% had known POLE mutation and TP53 mutation status
- 86% had known HRR mutation status
- 86% had evaluable BRCA mutation status
Overall, 84% of patients had positive expression for one or more biomarkers, with PD-L1–positive disease (67%) and TP53 mutations (59%) being the most prevalent.
Among the 284 patients evaluable for ctDNA status, 79% had detectable ctDNA, with detection rates higher than 65% across all relevant biomarker subgroups.
Safety Profile
The safety profiles in the pMMR subpopulation were generally consistent with previous reports in the ITT population. Adverse effects (AEs) occurred in nearly all patients across treatment arms:
- Chemotherapy arm: 100% experienced any AE, with 51% requiring dose interruptions or delays
- Chemotherapy plus durvalumab arm: 98% experienced any AE, with 53% requiring dose interruptions or delays
- Chemotherapy plus durvalumab/olaparib arm: 99% experienced any AE, with 66% requiring dose interruptions or delays
Clinical Implications
"[The analysis] does reinforce the potential for olaparib to be added to durvalumab safely and with efficacy across this biomarker group of [pMMR endometrial cancer]," Dr. Moore concluded.
These findings are particularly significant as pMMR endometrial cancer has historically been less responsive to immunotherapy alone compared to dMMR (mismatch repair-deficient) disease. The addition of olaparib to the treatment regimen appears to overcome some of these limitations, providing a potential new therapeutic approach for this patient population.
The consistent benefit across multiple biomarker subgroups suggests that this combination therapy could be broadly applicable to patients with pMMR endometrial cancer, potentially changing treatment paradigms for this disease.
