The purpose of this study is to evaluate the efficacy and safety of selinexor as a maintenance treatment in patients with p53 wt endometrial carcinoma (EC), who have achieved a partial response (PR) or complete response (CR) (per Response Evaluation Criteria in Solid Tumors version 1.1 \[RECIST v 1.1\]) after completing at least 12 weeks of platinum-based therapy. A total of 276 participants will be enrolled in the study and randomized in a 1:1 ratio to maintenance therapy with either selinexor or placebo.