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.

Inclusion Criteria: Patients must meet all of the following inclusion criteria in order to be eligible to participate in this study:

• Adults (Aged ≥ 18 years)
• Histologically confirmed endometrial cancer (endometrioid, serous, undifferentiated, or carcinosarcoma sub-types) that is TP53 wild type by central NGSHistologically confirmed EC including endometrioid, serous, undifferentiated, and carcinosarcoma
• Must have completed at least 12 weeks of platinum-based chemotherapy (with or without immune checkpoint inhibitors), with a confirmed partial or complete response according to RECIST v1.1
• Must be able to initiate C1D1 within 3-8 weeks after last platinum dose
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• Adequate bone marrow function and organ function

Exclusion Criteria: Patients meeting any of the following exclusion criteria are not eligible to participate in this study:

• Uterine sarcomas, clear cell or small cell carcinoma with neuroendocrine differentiation
• Palliative radiotherapy administered within 14 days of intended C1D1
• Any gastrointestinal dysfunction that could interfere with the absorption of oral study therapy
• Serious psychiatric or medical conditions that could interfere with study participation or would make study involvement unreasonably hazardous
• Previous treatment with an XPO1 inhibitor
• Stable disease or disease progression after platinum-based chemotherapy
• Pregnancy, breastfeeding, or other legal/ethical restrictions to trial participation
• Known dMMR/MSI-H EC tumors that are medically eligible to receive an immune checkpoint inhibitor

Female

Double blind placebo-controlled study