['metastatic triple negative breast cancer']
['capecitabine', 'eribulin', 'gemcitabine', 'vinorelbine']

        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
      