Objectives Pembrolizumab, an anti–PD-1 antibody, has demonstrated activity as monotherapy and in combination with lenvatinib in patients with previously treated mismatch repair (MMR) deficient and MMR proficient endometrial cancer (EC). ENGOT-en11/GOG-3053/KEYNOTE-B21 (NCT04634877) is a phase 3, randomized, double-blind study of pembrolizumab or placebo in combination with adjuvant chemotherapy with/without radiotherapy in patients with EC.

Methods Eligible patients are ≥18 years with newly diagnosed high-risk (stage I/II non-endometrioid or with p53 abnormality and any histology, stage III/IVa), previously untreated EC following surgery with curative intent with no evidence of disease post-operatively. ∼990 patients will be randomized to receive pembrolizumab 200 mg or placebo Q3W for 6 cycles plus chemotherapy (carboplatin area under the curve [AUC] 5/6 plus paclitaxel 175 mg/m² Q3W or carboplatin AUC 2/2.7 plus paclitaxel 60 mg/m² QW) in stage 1. Patients receive pembrolizumab 400 mg or placebo Q6W for 6 cycles in stage 2. Radiotherapy (external beam radiotherapy [EBRT] and/or brachytherapy) ± radiosensitizing cisplatin 50 mg/m² (days 1 and 29) may be administered after completion of chemotherapy. Randomization is stratified by MMR status (pMMR vs dMMR) and, within pMMR, by planned radiation therapy (cisplatin-EBRT vs EBRT vs no EBRT), histology (endometrioid vs non-endometrioid), and FIGO surgical stage (I/II vs III/IVA). Dual primary endpoints are disease-free survival (DFS; per investigator assessment) and OS. Secondary endpoints include DFS (per BICR), DFS (per investigator assessment) and OS by biomarker status (PD-L1 and tumor mutational burden), safety, and QoL. Enrollment began December 2020 and is ongoing in 28 countries.

Results Not applicable

Conclusions Not applicable