Dostarlimab in advanced/recurrent (AR) mismatch repair deficient/microsatellite instability–high or proficient/stable (dMMR/MSI-H or MMRp/MSS) endometrial cancer (EC): The GARNET study.
Ana Oaknin, Bhavana Pothuri, Lucy Gilbert, Renaud Sabatier, SharadA. Ghamande, Adriano Gravina, Emiliano Calvo, Susana Banerjee, Rowan Miller, Joanna Pikiel, MansoorRaza Mirza, Tao Duan, S. Zildjian, Eleftherios Zografos, JenniferLynnTaylor Veneris, Anna V. Tinker
Abstract
5509 Background: Dostarlimab is a programmed death 1 (PD-1) inhibitor approved in the U.S. as a monotherapy in patients (pts) with dMMR AR EC that has progressed on or after treatment with a platinum-containing regimen or dMMR solid tumors that have progressed on or after prior treatment, with no satisfactory alternative treatment options; and in the E.U. as a monotherapy in pts with dMMR/MSI-H AR EC that has progressed on or after treatment with a platinum-containing regimen. Here, we report on efficacy and safety in the 2 expansion cohorts of the GARNET trial that enrolled pts with EC. Methods: GARNET is a multicenter, open-label, single-arm phase 1 study. Pts were assigned to cohort A1 (dMMR/MSI-H EC) or cohort A2 (MMRp/MSS EC) based on local assessment. Pts received 500 mg of dostarlimab IV Q3W for 4 cycles, then 1,000 mg Q6W until disease progression, discontinuation, or withdrawal. The primary endpoints are ORR and DOR by blinded independent central review using RECIST v1.1. Results: For this third interim analysis, 153 dMMR/MSI-H and 161 MMRp/MSS pts were enrolled and dosed. Of these, 143 dMMR/MSI-H and 156 MMRp/MSS pts had measurable disease at baseline and ≥ 6 mo of follow-up and were included in the efficacy-evaluable population. ORRs were 45.5% (dMMR/MSI-H) and 15.4% (MMRp/MSS; Table). Median (m) DORs were not reached (NR; dMMR/MSI-H) and 19.4 mo (MMRp/MSS). Probability of PFS at 6, 9, and 12 mo was 49.5%, 48.0%, and 46.4% in dMMR/MSI-H EC and 35.8%, 31.3%, and 29.4% in MMRp/MSS EC, respectively. mOS was NR (dMMR/MSI-H) and 16.9 mo (MMRp/MSS). Overall, 27 pts (8.6%) discontinued treatment because of a treatment-related adverse event (TRAE; 13 dMMR/MSI-H, 14 MMRp/MSS). The majority of TRAEs were grade 1 or 2. The most common any-grade TRAEs were fatigue (56; 17.8%), diarrhea (46; 14.6%), and nausea (43; 13.7%). No deaths were attributed to dostarlimab in the EC cohorts. Hypothyroidism (12; 8%) was the most common any-grade immune-related TRAE. Conclusions: Dostarlimab demonstrated durable antitumor activity in both dMMR/MSI-H and MMRp/MSS AR EC. dMMR/MSI-H was associated with better outcomes: a higher response rate and longer PFS and OS. Safety was consistent with other PD-1 antibodies. Clinical trial information: NCT02715284. [Table: see text]