The study will consist of two parts.
In Part 1, the safety of pembrolizumab (MK-3475) in combination with one of three different chemotherapies will be assessed in the treatment of locally recurrent inoperable or metastatic triple negative breast cancer (TNBC), which has not been previously treated with chemotherapy.
In Part 2, the safety and efficacy of pembrolizumab plus chemotherapy will be assessed compared to the safety and efficacy of placebo plus chemotherapy in the treatment of locally recurrent inoperable or metastatic TNBC, which has not been previously treated with chemotherapy.
The primary hypotheses are that:
the combination of pembrolizumab and chemotherapy prolongs Progression-Free Survival (PFS) compared to placebo and chemotherapy in:
all participants,
participants with programmed cell death-ligand 1 (PD-L1) combined positive score (CPS) ≥1 tumors, and
participants with PD-L1 CPS ≥10 tumors, and
the combination of pembrolizumab and chemotherapy prolongs Overall Survival (OS) compared to placebo and chemotherapy in:
all participants,
participants with PD-L1 CPS ≥1 tumors, and
participants with PD-L1 CPS ≥10 tumors.
