Safety of dostarlimab in combination with chemotherapy in patients with primary advanced or recurrent endometrial cancer in a phase III, randomized, placebo-controlled trial (ENGOT-EN6-NSGO/GOG-3031/RUBY).

Background: In Part 1 of the phase III RUBY trial (NCT03981796) in patients with primary advanced or recurrent endometrial cancer (EC), dostarlimab plus carboplatin-paclitaxel (CP) significantly improved progression-free survival and overall survival compared with CP alone. Limited safety data have been reported for the combination of immunotherapies plus chemotherapy in this setting.

Objectives: The objective of this analysis was to identify the occurrence of treatment-related adverse events (TRAEs) and immune-related adverse events (irAEs) and to describe irAE management in Part 1 of the RUBY trial.

Design: RUBY is a phase III, randomized, double-blind, multicenter study of dostarlimab plus CP compared with CP alone in patients with primary advanced or recurrent EC.

Methods: Patients were randomized 1:1 to dostarlimab 500 mg, or placebo, plus CP every 3 weeks for 6 cycles, followed by dostarlimab 1000 mg, or placebo, every 6 weeks for up to 3 years. Adverse events (AEs) were assessed according to Common Terminology Criteria for Adverse Events, version 4.03.

Results: The safety population included 487 patients who received ⩾1 dose of treatment (241 dostarlimab plus CP; 246 placebo plus CP). Treatment-emergent AEs were experienced by 100% of patients in both arms. TRAEs occurred in 97.9% of the dostarlimab arm and 98.8% of the placebo arm.The most common TRAEs occurred at similar rates between arms and were mostly low grade. IrAEs occurred in 58.5% of patients in the dostarlimab arm and 37.0% of patients in the placebo arm. Dostarlimab- or placebo-related irAEs were reported in 40.7% of patients in the dostarlimab arm and 16.3% of the placebo arm.

Conclusion: The safety profile of dostarlimab plus CP was generally consistent with that of the individual components. Dostarlimab plus CP has a favorable benefit-risk profile and is a new standard of care for patients with primary advanced or recurrent EC.

Trial Registration: NCT03981796.