The goal of this clinical trial is to understand the effectiveness of dostarlimab and carboplatin-paclitaxel followed by dostarlimab monotherapy in participants with endometrial cancer

Inclusion Criteria:

1. Participant has histologically or cytologically proven endometrial cancer with recurrent or advanced disease.
2. Participant has molecular subtype of defective mismatch repair/microsatellite instability high (dMMR/MSI-H) or mismatch repair proficient/microsatellite stable (MMRp/MSS) determined.
3. Participant must have primary Stage III or Stage IV disease or first recurrent endometrial cancer with a low potential for cure by radiation therapy or surgery alone or in combination, and presence of at least one measurable lesion per RECIST 1.1 based on Investigator's assessment.
4. Participant is not pregnant or breastfeeding and agrees to use a highly effective contraceptive method during the study period if a woman of childbearing potential (WOCBP).
5. Participant has an Eastern Cooperative Oncology Group Performance status (ECOG PS) of 0 or 1.
6. Participant has adequate organ function, as assessed by hematologic, renal, hepatic and coagulation parameters.

Exclusion Criteria:

1. Participant has a concomitant malignancy, or participant has a prior non-endometrial invasive malignancy who has been disease-free for <3 years or who received any active treatment in the last 3 years for that malignancy. Non-melanoma skin cancer is allowed.
2. Participant has any medical history of interstitial lung disease or pneumonitis.
3. Participant has cirrhosis or current unstable liver or biliary disease.
4. Participant has known uncontrolled central nervous system metastases, carcinomatosis meningitis, or both.
5. Participant has a diagnosis of immunodeficiency.
6. Participant has received prior therapy with an anti- Programmed death protein 1 (PD-1), anti- Programmed death ligand 1 (PD-L1), anti- Programmed death ligand 2 (PD-L2), or anti- Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) agent.
7. Participant has not recovered adequately from AEs.
8. Participant has received prior anticancer therapy (chemotherapy, targeted therapies, hormonal therapy, radiotherapy, or immunotherapy) within 21 days or <5 times the half-life of the most recent therapy prior to the first dose of study intervention, whichever is shorter.
9. Participant has received any live vaccine within 30 days of the first dose of study intervention. Vaccination against coronavirus disease 2019 (COVID-19) using vaccines that are authorized via the appropriate regulatory mechanisms are not exclusionary.
10. Participant has HBsAg positive, or HCV RNA positive.
11. Participant is known HIV infection.
12. Participant is currently participating and receiving study intervention or has participated in a study of an investigational agent and received study intervention or used an investigational device within 4 weeks of the first dose of treatment.
13. Participant with contraindication to carboplatin and paclitaxel.

Female

Qualified researchers may request access to anonymized individual patient-level data (IPD) and related study documents of the eligible studies via the Data Sharing Portal. Details on GSK's data sharing criteria can be found at: https://www.gsk.com/en-gb/innovation/trials/data-transparency/

Anonymized IPD will be made available within 6 months of publication of primary, key secondary and safety results for studies in product with approved indication(s) or terminated asset(s) across all indications.

Anonymized IPD is shared with researchers whose proposals are approved by an Independent Review Panel and after a Data Sharing Agreement is in place. Access is provided for an initial period of 12 months but an extension may be granted, when justified, for up to 6 months.