XPORT: This study is evaluating whether giving a drug called selinexor as maintenance therapy is safe and effective in people with p53 Wild-Type advanced or recurrent endometrial cancer who have had prior treatment with platinum-based therapyA Phase 3, 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

Inclusion

• At least 18 years of age at the time of signing informed consent.
• Histologically confirmed EC including: endometrioid, serous, undifferentiated, and carcinosarcoma.
• TP53 wt assessed by next generation sequencing (NGS), evaluated by a central vendor.
• Completed a single line, at least 12 weeks of platinum-based therapy (not including adjuvant or neoadjuvant therapy for Stage I-III disease) and achieved confirmed partial or complete response (PR or CR) by imaging, according to RECIST version 1.1. The participants should have received treatment for:

Primary Stage IV disease, defined as:

• had a primary or later debulking surgery during first-line platinum-based therapy with R0 resection (R0 resection indicates a macroscopic complete resection of all visible tumor) and achieved CR after at least 12 weeks platinum-based therapy, OR
• had a primary or later debulking surgery during first-line platinum-based therapy with R1 resection (R1 resection indicates incomplete removal of all macroscopic disease) and achieved PR or CR after at least 12 weeks platinum-based chemotherapy, OR
• had no surgery and achieved PR or CR after at least 12 weeks platinum-based chemotherapy

OR

At first relapse (i.e., relapse after primary therapy including surgery and/or chemotherapy and/or immunotherapy for Stage I-IV disease), defined as:

• had Stage I - III disease at diagnosis and received, at initial diagnosis, adjuvant chemotherapy and relapsed later. Participants should have PR or CR after at least 12 weeks of platinum-based chemotherapy compared with the start of this chemotherapy at the time of relapse,
• had Stage I-III disease at diagnosis and did not receive adjuvant chemotherapy at initial diagnosis and relapsed later. Participants should have PR or CR after at least 12 weeks of platinum-based chemotherapy compared with the start of this chemotherapy at the time of relapse, OR

• had Stage IV disease at diagnosis and received initially chemotherapy with or without surgery and relapsed later. At the time of relapse, participants should have PR or CR after at least 12 weeks of platinum-based chemotherapy compared with the start of this chemotherapy at the time of relapse.

  • Previous treatment with anti-programmed cell death protein 1(PD-1) or anti-programmed death-ligand 1(PD-L1) monoclonal antibody and concomitant biologic agents (e.g., bevacizumab, trastuzumab) is allowed.
  • Must be able to initiate study drug 3 to 8 weeks after completion of their final dose of chemotherapy.
  • Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
  • Participants must have adequate bone marrow function and organ function within 2 weeks before starting study drug as defined by the following laboratory criteria:
• Hepatic function: total bilirubin up to less than (<) 3*upper limit of normal (ULN); alanine aminotransferase (ALT) and aspartate aminotransferase (AST) less than or equal to (<=) 2.5*ULN in participants without liver metastasis. For participants with known liver involvement of their tumor: AST and ALT (<=) 5*ULN
• Hematopoietic function within 1 week: Absolute neutrophil count (ANC) greater than or equal to (>=) 1.5*10^9/liter (L); platelet count >= 100*10^9/L; hemoglobin >= 9.0 gram per deciliter (g/dL) per local laboratory results

• Renal function: estimated creatinine clearance (CrCl) of >= 20 milliliter per minute (mL/min), calculated using the standard local formula, as applicable

  - In the opinion of the Investigator, the participant must:

• Have a life expectancy of at least 12 weeks, and

• Be fit to receive investigational therapy

  • Premenopausal females of childbearing potential must have a negative pregnancy test (serum β-human chorionic gonadotropin test) prior to the first dose of study drug. Female participants of childbearing potential must agree to use highly effective methods of contraception throughout the study and for 90 days following the last dose of study drug.
  • Written informed consent signed in accordance with federal, local, and institutional guidelines prior to the first screening procedure.