Deficient mismatch mutation repair mechanisms may sensitize endometrial cancers to anti-programmed death 1 (PD-1) therapies. Dostarlimab (TSR-042) is an investigational anti-PD-1 antibody that binds with high affinity to the PD-1 receptor.To assess the antitumor activity and safety of dostarlimab for patients with deficient mismatch repair endometrial cancer.This ongoing, open-label, single-group, multicenter study began part 1 on March 7, 2016, and began enrolling patients with deficient mismatch mutation repair endometrial cancer on May 8, 2017. Median follow-up was 11.2 months (range, 0.03 [ongoing] to 22.11 [ongoing] months; based on radiological assessments). Statistical analysis was performed July 8 to August 9, 2019.Patients received 500 mg of dostarlimab intravenously every 3 weeks for 4 doses, then 1000 mg every 6 weeks until disease progression, treatment discontinuation, or withdrawal.The primary end point was objective response rate and duration of response by blinded independent central review using Response Evaluation Criteria in Solid Tumors, version 1.1.As of the data cutoff, 104 women (median age, 64.0 years [range, 38-80 years]) with deficient mismatch mutation repair endometrial cancers were enrolled and treated with dostarlimab. Of these, 71 had measurable disease at baseline and at 6 months or more of follow-up and were included in the analysis. There was a confirmed response in 30 patients (objective response rate, 42.3%; 95% CI, 30.6%-54.6%); 9 patients (12.7%) had a confirmed complete response, and 21 patients (29.6%) had a confirmed partial response. Responses were durable; the median duration of response was not reached (median follow-up was 11.2 months). The estimated likelihood of maintaining a response was 96.4% at 6 months and 76.8% at 12 months. Anemia (3 of 104 [2.9%]), colitis (2 of 104 [1.9%]), and diarrhea (2 of 104 [1.9%]) were the most common grade 3 or higher treatment-related adverse events.In this nonrandomized trial, dostarlimab was associated with clinically meaningful and durable antitumor activity with an acceptable safety profile for patients with deficient mismatch mutation repair endometrial cancers after prior platinum-based chemotherapy.ClinicalTrials.gov identifier: NCT02715284.

Clinical Activity and Safety of the Anti–Programmed Death 1 Monoclonal Antibody Dostarlimab for Patients With Recurrent or Advanced Mismatch Repair–Deficient Endometrial Cancer