Phase 2b, open-label, single-arm, multicenter pilot study of the efficacy, safety, and tolerability of dostarlimab in women with early-stage mismatch repair-deficient endometrioid endometrial adenocarcinoma

Abstract

Background: The standard treatment for endometrial cancer is hysterectomy with or without bilateral salpingo-oophorectomy; however, this may not be an optimal choice for women who have not completed childbearing or who are at a high risk of surgical complications. Conservative treatment with levonorgestrel intrauterine devices appear to be effective in patients with early-stage endometrial cancer; however, patients with mismatch repair-deficient (dMMR) tumors have a low likelihood of responding to levonorgestrel intrauterine devices.

Primary objective: To assess the efficacy of dostarlimab, an active immune checkpoint inhibitor that targets the programmed cell death protein-1 receptor, in patients with early-stage dMMR endometrioid endometrial adenocarcinoma.

Study hypothesis: Administration of 4 3-weekly cycles of 500 mg dostarlimab followed by a 3-week rest period and 3 6-weekly cycles of 1000 mg dostarlimab will be safe and efficacious in early-stage dMMR endometrial cancer patients.

Trial design: Non-randomized, open-label, pilot, multicenter phase2b study designed to evaluate the efficacy and safety of dostarlimab in 10 women aged ≥18 years with a clinically confirmed diagnosis of early-stage and dMMR endometrioid endometrial adenocarcinoma.

Major inclusion/exclusion criteria: Eligible patients must have histologically proven stage I, International Federation of Gynecology and Obstetrics grade 1 or 2 dMMR endometrioid endometrial adenocarcinoma and desire for fertility preservation. Exclusions include, but are not limited to, patients with other high-risk endometrial cancer cell types, a poor medical risk due to uncontrolled medical conditions, or those who experienced grade 3 or higher immune-related adverse events from prior immunotherapy.

Primary endpoint(s): The primary endpoint is the number of participants achieving investigator-assessed pathological complete response within 6 months of treatment.

Sample size: Ten (10) women ≥18 years of age will be enrolled.

Estimated dates for completing accrual and presenting results: Accruals are expected to be completed by 2027, with the presentation of results by 2029.

Trial registration: NCT06278857.

Keywords: Dostarlimab; Endometrial cancer; Fertility-sparing treatment; Mismatch repair.