The goal of this clinical trial is to see how well dostarlimab works when administered with the chemotherapy drugs carboplatin and paclitaxelin in treating EC in Chinese participants. The study aims to understand the treatments effectiveness, safety, how the drugs behave in the body, and whether it causes any immune reactions.

Inclusion Criteria:

1. Participant has histologically or cytologically proven EC with recurrent or advanced disease.

2. Participant has molecular subtype of defective mismatch repair (dMMR) or microsatellite instability high (MSI-H) determined by the central reference laboratory before study intervention.

3. Participant must have primary Stage III or Stage IV disease or first recurrent EC with a low potential for cure by radiation therapy or surgery alone or in combination, and presence of at least one target lesion per RECIST 1.1 based on Investigator's assessment and meet at least 1 of the following criteria:

   1. Has primary Stage III to IV disease and is naive to systemic anticancer therapy for EC;
   2. Has first recurrent disease and is naïve to systemic anticancer therapy for EC;
   3. Had received prior neo-adjuvant/adjuvant anticancer therapy and had a recurrence or PD ≥6 months after completing treatment (first recurrence only).

4. Participant has adequate archive tumor tissue sample for MMR/MSI status testing. If no archival tissue is available, tissue sample must be obtained before study intervention.

5. 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).

6. Participant has an Eastern Cooperative Oncology Group Performance status (ECOG PS) of 0 or 1.

7. 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 prior to the first dose of study intervention.
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 Hepatitis B surface antigen (HBsAg) positive, or Hepatitis C virus (HCV) Ribonucleic acid (RNA) positive at screening or within 3 months prior to the first dose of study intervention.
11. Participant is known human immunodeficiency virus (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.

Study Sponsor will assess requests from qualified researchers for anonymized individual patient-level data and related study documents. Data sharing is subject to certain criteria, conditions, and exceptions. For further information, refer to https://www.gsk-studyregister.com/About\_GSK\_Patient\_Level\_Data\_Sharing\_Final\_13July2023.pdf

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 asset(s) with development terminated 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.