427956 Background: Molecular characterization is important to inform treatment decisions for patients with endometrial cancer (EC). Wild type TP53 (TP53wt) is found in ~75% of newly diagnosed EC and 50% of advanced/recurrent tumors; there are no specific targeted therapies available for patients with TP53wt EC. Selinexor is an investigational oral XPO1 inhibitor that drives nuclear retention and functional activation of wild type tumor suppressor proteins, including p53. Methods: SIENDO (NCT03555422) was a phase 3 double-blind study evaluating selinexor vs placebo as maintenance therapy in patients with advanced/recurrent EC following response to prior systemic therapy. The primary endpoint was progression-free survival (PFS), which was previously presented at the ESMO plenary in March 2022. Preliminary analysis of a pre-specified exploratory subgroup of patients with TP53wt EC showed a decrease in risk for progression or death with a median PFS of 13.7 months with selinexor as mainten