Study Keyword: Programmed Cell Death Receptor 1

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.