A Study to Compare Sacituzumab Tirumotecan (MK-2870) in Combination With Pembrolizumab (MK-3475) Versus Pembrolizumab Alone as Treatment in Participants With Mismatch Repair Proficient Endometrial Cancer (MK-2870-033/TroFuse-033/GOG-3119/ENGOT-en29)

All participants undergo an initial Induction Phase of six cycles, each cycle consisting of pembrolizumab + carboplatin + paclitaxel or docetaxel. Each cycle is three weeks. Participants whose cancer does not progress enter the Maintenance Treatment Phase and are then randomly assigned to pembrolizumab + sac-TMT or pembrolizumab monotherapy. Participants whose cancer does progress will have the possibility to enter the Subsequent Treatment Phase and are then randomly assigned to pembrolizumab + sac-TMT or sac-TMT monotherapy.

Key inclusion criteria include but are not limited to:

• Has a histologically confirmed diagnosis of primary advanced or recurrent endometrial carcinoma that has been confirmed as proficient mismatch repair (pMMR)
• Has radiographically evaluable disease, with measurable Stage III or either measurable or non-measurable Stage IV or recurrent disease per Response Evaluation Criteria In Solid Tumors version 1.1 (RECIST 1.1), as assessed by the investigator
• Has received no prior systemic therapy for endometrial carcinoma except the following conditions as pre-specified by the protocol: 1 prior line of systemic platinum-based adjuvant and/or neoadjuvant chemotherapy in the setting of curative-intent, prior radiation with or without radiosensitizing chemotherapy if >2 weeks before the start of induction treatment, or prior hormonal therapy for treatment of endometrial carcinoma that was discontinued ≥1 week before the start of induction treatment

Key exclusion criteria include but are not limited to:

• Has carcinosarcoma, neuroendocrine tumors or endometrial sarcoma, including stromal sarcoma, leiomyosarcoma, adenosarcoma, or other types of sarcomas
• Has endometrial carcinoma of any histology that is mismatch repair deficient (dMMR)
• Is a candidate for debulking surgery resulting in complete removal of all tumor and no evidence of radiological disease following surgery, or curative-intent radiotherapy at the time of enrollment
• Has a history of documented severe dry eye syndrome, severe Meibomian gland disease and/or blepharitis, or severe corneal disease that prevents/delays corneal healing
• Has active inflammatory bowel disease requiring immunosuppressive medication or previous history of inflammatory bowel disease
• Has uncontrolled, significant cardiovascular disease or cerebrovascular disease
• Human Immunodeficiency Virus-infected participants with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease
• Received prior therapy in any setting with any of the following: anti-programmed cell death 1 protein, anti-programmed cell death ligand 1, anti-programmed cell death ligand 2 agent, or with an agent directed to another stimulatory or coinhibitory T-cell receptor; trophoblast cell surface antigen 2-targeted antibody drug conjugate; or topoisomerase I inhibitor-containing antibody drug conjugate