Background: In RUBY (NCT03981796), a phase 3, global, randomized, double-blind trial, D+CP demonstrated significant and clinically meaningful improvement in PFS vs placebo + CP (P+CP) in pA/rEC. Methods: 494 pts with pA/rEC were randomized 1:1 to D+CP or P+CP Q3W for 6 cycles (C), followed by D or placebo monotherapy Q6W for ≤2 y. EORTC QLQ-C30 and EN24 (prespecified secondary endpoints) were administered on day 1 of each C, at end of treatment (EOT), and at safety and survival follow-ups. Change (chg) from baseline (BL) to C7 (end of chemotherapy) and C13 (1 y) was calculated in the overall and mismatch repair–deficient (dMMR)/microsatellite instability–high (MSI-H) populations. Least-squares means (LSM) were generated using mixed models for repeated measures, adjusting for correlations across multiple assessments within a pt and controlling for BL global, pain, fatigue, and physical function (PF) scores. Results: In the overall population, PROs were similar with D+CP and P+CP through C7, and no differences between arms across the 3-y period were reported; mean chg from BL to EOT showed numerical improvement with D+CP in back/pelvic pain and deterioration with P+CP in global QOL/GHS, social function (SF), body image, and chg in taste. In the dMMR/MSI-H population, at C7, nominally significant improvements in QOL, PF, role function (RF), pain, and back/pelvic pain were seen with D+CP vs P+CP (Table). Conclusions: Dostarlimab+CP significantly improved PFS and maintained HRQOL in dMMR/MSI-H and overall populations, further supporting its use as a standard of care in pA/rEC. Clinical trial information: NCT03981796.

^aNominally significant LSM difference between arms (P<.05). ^bLower scores indicate reduced symptom severity.