Overall Survival in Patients with Endometrial Cancer Treated with Dostarlimab plus Carboplatin-Paclitaxel in the Randomized ENGOT-EN6/GOG-3031/RUBY Trial

Background Part 1 of the RUBY trial (NCT03981796) evaluated dostarlimab plus carboplatin-paclitaxel compared with placebo plus carboplatin-paclitaxel in patients with primary advanced or recurrent endometrial cancer. At the first interim analysis, the trial met one of its dual-primary endpoints with statistically significant progression-free survival benefits in the mismatch repair deficient/microsatellite instability–high (dMMR/MSI-H) and overall populations. Overall survival (OS) results are reported from the second interim analysis. Patients and Methods RUBY is a phase 3, global, double-blind, randomized, placebo-controlled trial. Part 1 of RUBY enrolled eligible patients with primary advanced stage III or IV or first recurrent endometrial cancer who were randomly assigned (1:1) to receive either dostarlimab (500 mg) or placebo, plus carboplatin-paclitaxel every 3 weeks for 6 cycles followed by dostarlimab (1000 mg) or placebo every 6 weeks for up to 3 years. OS was a dual-primary endpoint. Results A total of 494 patients were randomized (245 in dostarlimab arm; 249 in placebo arm). In the overall population, with 51% maturity, RUBY met the dual-primary endpoint for OS at this second interim analysis, with a statistically significant reduction in the risk of death (HR = 0.69; 95% CI, 0.54-0.89; P = 0.0020) in patients treated with dostarlimab plus carboplatin-paclitaxel versus carboplatin-paclitaxel alone. The risk of death was lower in the dMMR/MSI-H population (HR = 0.32; 95% CI, 0.17-0.63; nominal P = 0.0002) and a trend in favor of dostarlimab was seen in the mismatch repair proficient/microsatellite stable (MMRp/MSS) population (HR = 0.79; 95% CI, 0.60-1.04; nominal P = 0.0493). The safety profile for dostarlimab plus carboplatin-paclitaxel was consistent with the first interim analysis. Conclusions Dostarlimab in combination with carboplatin-paclitaxel demonstrated a statistically significant and clinically meaningful overall survival benefit in the overall population of patients with primary advanced or recurrent endometrial cancer while demonstrating an acceptable safety profile.