Condition: Breast Neoplasms

The safety and efficacy of pembrolizumab plus the investigator’s choice of chemotherapy will be assessed compared to placebo plus the investigator’s choice of chemotherapy in the treatment of chemotherapy-candidate hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) locally recurrent inoperable or metastatic breast cancer.

The primary hypotheses are that the combination of pembrolizumab and chemotherapy is superior to placebo and chemotherapy in regards to Progression-Free Survival (PFS) or overall survival (OS) in participants with programmed cell death-ligand 1 (PD-L1) combined positive score (CPS) ≥1 and ≥10.