The benefit of the combination of the programmed death protein 1 (PD-1) inhibitor dostarlimab (Jemperli) and chemotherapy was even more pronounced among patients with DNA mismatch repair deficient/microsatellite instability high (dMMR/MSI-H) tumors.
These results, from the second interim analysis of the phase 3 ENGOT-EN6-NSGO/GOG-3031/RUBY trial, were cheered by audience members when they were reported at the Society of Gynecologic Oncology (SGO)’s Annual Meeting on Women’s Cancer, held in San Diego, California.
“Overall survival benefit to the addition of PD-1 inhibitor to chemotherapy upfront for patients with advanced and recurrent MSI-high endometrial cancer: SOLD!” said invited discussant Gini Fleming, medical director of gynecologic oncology at the University of Chicago.
“I think this is a huge win for our patients. It’s something that none of us have seen before over many years of working with endometrial cancer and should be incorporated into everybody’s practice as of yesterday,” she said.
Continued Improvement
Results from the first interim analysis of the trial showed that dostarlimab and chemotherapy significantly improved progression-free survival (PFS) in the dMMR/MSI-H population, and there was an early trend toward improved overall survival, compared with chemotherapy plus placebo.
As Matthew A. Powell, MD from Washington University School of Medicine in Saint Louis, Missouri reported at SGO 2024, that early trend has become an undeniable survival advantage.
At a median follow-up of 37.2 months, the median overall survival was 44.6 months for patients randomized to the combination, compared with 28.2 months for those assigned to chemotherapy plus placebo.
The respective 3-year overall survival (OS) rates were 54.9% and 42.9%, translating into a hazard ratio (HR) for death with dostarlimab/chemotherapy of 0.69 (P = .002).
Among the subset of patients with dMMR/MSI-H tumors the survival benefit conferred by the combination was even greater, with median OS not reached in the dostarlimab group vs 31.4 months in the chemotherapy-alone arm, with respective 3-year OS rates of 78% and 46%. This difference translated into a HR for death with the combination of 0.32 (P = .0002) for patients with deficient mismatch-repair cancers.
“Dostarlimab plus carboplatin-paclitaxel chemotherapy demonstrated statistically significant and clinically meaningful overall survival improvements in the overall population, a substantial unprecedented overall survival benefit in patients with defective mismatch-repair tumors, and a clinically meaningful; 7-month improvement in the OS difference in patients with proficient mismatch-repair tumors,” Dr. Powell said.
RUBY Details
The trial was conducted in 494 patients with primary advanced stage III or IV or first recurrent endometrial cancer who received first-line treatment with standard chemotherapy with carboplatin (area under the concentration–time curve, 5 mg/mL per minute) and paclitaxel (175 mg/m2 of body surface area), every 3 weeks (six cycles). They were also randomized to receive either dostarlimab (1000 mg) or dostarlimab placebo every 6 weeks for up to 3 years.
Within the cohort, 118 patients (23.9%) had dMMR/MSI-H tumors.
At the time of the first interim analysis the estimated progression-free survival at 24 months in the dMMR–MSI-H subgroup was 61.4% in the dostarlimab group vs 15.7 in the placebo group (HR for progression or death, 0.28; P < .001). For the entire cohort, progression-free survival at 24 months was 36.1% vs 18.1% (HR, 0.64; P < .001).
A prespecified exploratory analysis of progression-free survival in proficient MMR, microsatellite stable (MSS) patients was also done, and a clinically relevant benefit was observed.
Overall survival at that time also favored dostarlimab, although it was only mature for 33% of the population. But at 24 months, OS rates were 71.3% vs 56.0% among placebo recipients; this difference approached but did not reach statistical significance.
The overall response rate in the dMMR–MSI-H population vs the placebo group was 77.6% vs 69%, respectively, and 68.1% and 63.4% in the pMMR/MSS population.
The most common adverse events observed were nausea, alopecia, and fatigue. Grade 3 and higher adverse events at the most recent follow-up were more frequent in the dostarlimab group than in the placebo group (72.2% vs 60.2%).
“Importantly, safety was maintained” at the second interim analysis, Dr. Powell said.
“No new safety signals were noted, no new deaths related to therapy were noted with the subsequent 1-year additional analysis time,” he said.