Long-term follow-up of efficacy and safety of selinexor maintenance treatment in patients with TP53wt advanced or recurrent endometrial cancer: A subgroup analysis of the ENGOT-EN5/GOG-3055/SIENDO study.

OBJECTIVE: To report long-term efficacy and safety of selinexor maintenance therapy in adults with TP53 wild-type (TP53wt) stage IV or recurrent endometrial cancer (EC) who achieved partial remission (PR) or complete remission (CR) following chemotherapy. METHODS: Analysis of the prespecified, exploratory subgroup of patients with TP53wt EC from the phase 3 SIENDO study was performed. Progression-free survival (PFS) benefit in patients with TP53wt EC and across other patient subgroups were exploratory endpoints. Safety and tolerability were also assessed. RESULTS: Of the 263 patients enrolled in the SIENDO trial, 113 patients had TP53wt EC; 70/113 (61.9%) had TP53wt/proficient mismatch repair (pMMR) EC, and 29/113 (25.7%) had TP53wt/deficient mismatch repair (dMMR) EC. As of April 1, 2024, the median PFS (mPFS) for TP53wt patients who received selinexor compared with placebo was 28.4 versus 5.2 months (36.8-month follow-up, HR 0.44; 95% CI 0.27-0.73). A benefit in mPFS was seen with selinexor versus placebo regardless of MMR status (patients with TP53wt/pMMR EC: 39.5 vs 4.9 months, HR 0.36; 95% CI 0.19-0.71; patients with TP53wt/dMMR EC: 13.1 vs 3.7 months, HR 0.49; 95% CI 0.18-1.34). Selinexor treatment was generally manageable, with no new safety signals identified. CONCLUSION: In the phase 3 SIENDO study, selinexor maintenance therapy showed a promising efficacy signal and a manageable safety profile in the prespecified subgroup of patients with TP53wt EC who achieved a PR or CR following chemotherapy. These results are being further evaluated in an ongoing randomized phase 3 trial (NCT05611931).

ENGOT-EN20/GOG-3083/XPORT-EC-042 - A phase III, randomized, placebo-controlled, double-blind, multicenter trial of selinexor in maintenance therapy after systemic therapy for patients with p53 wild-type, advanced, or recurrent endometrial carcinoma: rationale, methods, and trial design.

BACKGROUND: Patients with advanced/recurrent endometrial cancer have a poor prognosis and limited treatment options. Biomarkers such as tumor protein 53 (TP53) in endometrial cancer can integrate novel strategies for improved and individualized treatment that could impact patient outcomes. In an exploratory analysis of the phase III ENGOT-EN5/GOG-3055/SIENDO study of selinexor maintenance monotherapy 80 mg in advanced/recurrent endometrial cancer, a pre-specified subgroup of patients with TP53 wild type (wt) endometrial cancer showed preliminary activity at long-term follow-up with a generally manageable safety profile (median progression-free survival 27.4 months vs 5.2 months placebo, HR=0.41). PRIMARY OBJECTIVE: To evaluate the efficacy of selinexor compared with placebo as maintenance therapy in patients with advanced or recurrent TP53wt endometrial cancer. STUDY HYPOTHESIS: Selinexor administered at 60 mg weekly as maintenance therapy will show manageable safety and maintain efficacy in patients with TP53wt advanced/recurrent endometrial cancer after systemic therapy versus placebo. TRIAL DESIGN: This is a prospective, multicenter, double-blind, placebo-controlled, randomized phase III study designed to evaluate the efficacy and safety of selinexor as a maintenance therapy in patients with advanced or recurrent TP53wt endometrial cancer. MAJOR INCLUSION/EXCLUSION CRITERIA: Eligible patients must have histologically confirmed endometrial cancer, TP53wt confirmed by next-generation sequencing, completed at least 12 weeks of platinum-based therapy with or without immunotherapy, with confirmed partial response or complete response, and primary Stage IV disease or at first relapse. PRIMARY ENDPOINT: The primary endpoint is investigator-assessed progression-free survival per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 in the intent-to-treat population. SAMPLE SIZE: A total of 220 patients will be enrolled. ESTIMATED DATES FOR COMPLETING ACCRUAL AND PRESENTING RESULTS: Accrual is expected to be completed in 2024 with presentation of results in 2025. TRIAL REGISTRATION: NCT05611931.