Study of Single Agent Pembrolizumab (MK-3475) Versus Single Agent Chemotherapy for Metastatic Triple Negative Breast Cancer (MK-3475-119/KEYNOTE-119)

A Randomized Open-Label Phase III Study of Single Agent Pembrolizumab Versus Single Agent Chemotherapy Per Physician's Choice for Metastatic Triple Negative Breast Cancer (mTNBC) - (KEYNOTE-119)

In this study, participants with metastatic triple negative breast cancer (mTNBC) will be randomly assigned to receive either single agent pembrolizumab or single agent chemotherapy chosen by the treating physician (Treatment of Physician's Choice, TPC) in accordance with local regulations and guidelines, consisting of either capecitabine, eribulin, gemcitabine, or vinorelbine. The primary study hypothesis is that pembrolizumab extends overall survival compared to TPC.

Inclusion Criteria:

• Centrally confirmed Stage IV/M1 mTNBC
• Newly obtained tumor biopsy from metastatic site
• Central determination of programmed cell death ligand 1 (PD-L1) tumor status
• Received either one or two prior systemic treatments for metastatic breast cancer and have documented disease progression on or after the most recent therapy
• Previously treated with an anthracycline and/or taxane in the neoadjuvant/adjuvant or metastatic setting
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 within 10 days prior to study start
• Adequate organ function

Exclusion Criteria:

• Participation in another clinical trial within 4 weeks
• Monoclonal antibody (mAb) for direct anti-neoplastic treatment within 4 weeks
• Chemotherapy, targeted small molecule therapy, or radiation therapy within at least 2 weeks
• Active autoimmune disease that required systemic treatment in the past 2 years
• Diagnosed with immunodeficiency or receiving systemic steroid therapy or another form of immunosuppressive therapy within 7 days
• Known additional malignancy that required treatment or progressed in last 5 years
• Known active brain metastases and/or carcinomatous meningitis
• Prior therapy with an anti-programmed cell death (PD)-1, anti-PD-ligand-1 (anti-PD-L1), anti-PD-L2 agent or with an agent directed to another co-inhibitory T-cell receptor (e.g. cytotoxic T-lymphocyte associated protein 4 [CTLA-4], OX-40, CD137) or previously participated in any pembrolizumab (MK-3475) clinical studies