Study Start Date
- Age ≥18 years at the time of screening and female. - Histologically confirmed diagnosis of epithelial endometrial carcinoma. All histologies, including carcinosarcomas, will be allowed. Sarcomas will not be allowed. - Patient must have endometrial cancer in one of the following categories: 1. Newly diagnosed Stage III disease (measurable disease per RECIST 1.1 following surgery or diagnostic biopsy), 2. Newly diagnosed Stage IV disease (with or without disease following surgery or diagnostic biopsy) 3. Recurrence of disease where the potential for cure by surgery alone or in combination is poor. - Naïve to first line systemic anti-cancer treatment. For patients with recurrent disease only, prior chemotherapy is allowed only if it was administered in the adjuvant setting and there is at least 12 months from date of last dose of chemotherapy administered to date of subsequent relapse - FPPE tumor sample must be available for MMR evaluation. - Has Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 within 7 days of starting study treatment.