Clinical Summary: 

• Design/Population: Updated 4-year follow-up from the phase 3 RUBY trial evaluated dostarlimab plus carboplatin and paclitaxel vs placebo plus chemotherapy in patients with dMMR/MSI-H primary advanced or recurrent endometrial cancer. 
• Key Outcomes: Dostarlimab plus chemotherapy maintained significant progression-free and overall survival benefits, with durable remissions and sustained disease control observed across response categories. 
• Clinical Relevance: These findings suggest long-term disease control and potential curative benefit with dostarlimab-based therapy in patients with dMMR/MSI-H endometrial cancer.

Updated results from the phase 3 RUBY trial demonstrated that dostarlimab plus carboplatin and paclitaxel sustained survival benefit among patients with mismatch repair–deficient or microsatellite instability–high (dMMR/MSI-H) primary advanced or recurrent endometrial cancer.

These findings were presented by Vladyslav Sukhin, MD, PhD, National Medical University, Kharkiv, Ukraine, at the European Society for Medical Oncology (ESMO) Gynecological Cancers Congress in Copenhagen, Denmark. 

In this study, 118 patients were randomized 1:1 to receive either dostarlimab plus carboplatin and paclitaxel (n = 53) or placebo plus carboplatin and paclitaxel (n = 65) once every 3 weeks for 6 cycles, followed by dostarlimab or placebo monotherapy every 6 weeks for up to 3 years or until disease progression. Primary end points included progression-free survival (PFS) and overall survival (OS). 

At a median follow-up of 55.6 months, median PFS and OS were not reached in the dostarlimab arm. The 4-year OS rate was 72.8% in the dostarlimab arm and 40.3% in the placebo arm. The 4-year PFS rates were 57.9% and 15.7%, respectively. Only 4 new progression events were reported during the additional 2.5 years of follow-up since the primary PFS analysis. 

Confirmed complete responses were achieved in 32.1% of patients in the dostarlimab arm and 16.9% of patients in the placebo arm. Partial responses occurred in 32.1% and 40% of patients, respectively.

Among the 17 patients who achieved a complete response in the dostarlimab arm, only 3 subsequently experienced disease progression and 1 patient died. Notably, only 1 of 12 patients with a complete response at 1 year had experienced progression by the 4-year landmark analysis.

Long-term disease control was also observed among patients with partial responses and stable disease. Among the 30 patients who remained alive and progression-free at 1 year in the dostarlimab arm, 33.3% continued to have a complete response and 16.7% maintained a partial response at 4 years.

“At [4 years], median PFS and OS were not reached with [dostarlimab plus carboplatin and paclitaxel] in the dMMR/MSI-H population from RUBY,” concluded Dr Sukhin. “The high rate of durable remission suggests the potential for curative intent with [dostarlimab plus carboplatin and paclitaxel] in this pt population.”

Source: 

Sukhin VS, Herzog TJ, Gilbert L, et al. Sustained remission and long-term survival outcomes with dostarlimab plus chemotherapy in patients with dMMR/MSI-H primary advanced or recurrent endometrial cancer in the ENGOT-EN6-NSGO/GOG-3031/RUBY trial. Presented at ESMO Gynecological Cancers Congress. June 17-19, 2026. Copenhagen, Denmark. Abstract 71RO.