Endometrial cancer, the second most common gynecologic malignancy, is typically treated with carboplatin and paclitaxel, but outcomes remain poor. The Phase 3 RUBY trial evaluated adding the anti–PD-1 drug dostarlimab to this regimen in 494 patients with newly diagnosed advanced or recurrent disease.
Dostarlimab significantly improved results: in patients with mismatch repair–deficient or MSI-high tumors, the risk of progression or death dropped by 72% (HR 0.28), with 24-month progression-free survival of 61.4% versus 15.7% with placebo. Across all patients, risk reduction was 36% (HR 0.64). Benefits were smaller but still present in mismatch repair–proficient cases.
Adverse events were more frequent with dostarlimab, including Grade ≥3 reactions (70.5% vs 59.8%) and immune-related effects such as hypothyroidism, but quality of life remained similar. Overall, dostarlimab plus chemotherapy markedly improved outcomes, especially in dMMR–MSI-H endometrial cancer.