An Open-label, Randomized Phase 3 Study of MK-2870 as a Single Agent and in Combination With Pembrolizumab Versus Treatment of Physician's Choice in Participants With HR+/HER2- Unresectable Locally Advanced or Metastatic Breast Cancer

The purpose of this study is to compare sacituzumab tirumotecan as a single agent, and in combination with pembrolizumab, versus Treatment of Physician's Choice (TPC) in participants with hormone receptor positive/human epidermal growth factor receptor-2 negative (HR+/HER2-) unresectable locally advanced, or metastatic, breast cancer.

The primary hypotheses are that sacituzumab tirumotecan as a single agent and sacituzumab tirumotecan plus pembrolizumab are superior to TPC with respect to progression-free survival (PFS) per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1) by blinded independent central review (BICR) in all participants.