['head and neck squamous cell cancer']
['methotrexate', 'docetaxel']

        Inclusion Criteria:

          -  Has histologically- or cytologically-confirmed recurrent disease not amenable to
             curative treatment with local or systemic therapy, or metastatic (disseminated) head
             and neck squamous cell carcinoma of the oral cavity, oropharynx, hypopharynx, and
             larynx that is considered incurable by local therapies

          -  Failure of prior platinum therapy

          -  Radiographically-measurable disease based on RECIST 1.1

          -  Tumor tissue available for PD-L1 biomarker analysis

          -  Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

          -  Adequate organ function

          -  Female participants of childbearing potential must be willing to use 2 methods of
             birth control or abstain from heterosexual activity for the course of the study
             through 120 days after last dose of pembrolizumab or through 120-180 days after the
             last dose of docetaxel, methotrexate or cetuximab, acccording to local standard of
             care

          -  Male participants must agree to use an adequate method of contraception starting with
             the first dose of study therapy through 120 days after last dose of pembrolizumab or
             through 120-180 days after the last dose of docetaxel, methotrexate or cetuximab,
             acccording to local standard of care

        Exclusion Criteria

          -  Disease is suitable for local therapy administered with curative intent

          -  Currently participating in or has participated in a study of an investigational agent
             or using an investigational device within 4 weeks prior to randomization

          -  Previously treated with 3 or more systemic regimens given for recurrent and/or
             metastatic disease

          -  Diagnosis of immunodeficiency or receiving systemic steroid therapy or any other form
             of immunosuppressive therapy within 7 days prior to the first dose of study therapy

          -  Not recovered from adverse events due to therapy more than 4 weeks earlier

          -  Prior anti-cancer monoclonal antibody (mAb) therapy within 4 weeks prior to study Day
             1, or not recovered from adverse events due to agents administered more than 4 weeks
             earlier

          -  Prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2
             weeks prior to study Day 1

          -  Diagnosed and/or treated additional malignancy within 5 years of randomization, with
             the exception of curatively-treated basal cell or squamous cell carcinoma of the skin,
             and/or curatively-resected in situ cervical and/or breast cancers

          -  Active autoimmune disease that has required systemic therapy in the past 2 years with
             modifying agents, corticosteroids, or immunosuppressive agents

          -  Active central nervous system (CNS) metastases and/or carcinomatous meningitis

          -  Active, non-infectious pneumonitis

          -  Active infection requiring systemic therapy

          -  Pregnant, breastfeeding, or expecting to conceive or father children within the
             projected duration of the trial, starting with the screening visit through 120 days
             after the last dose of trial therapy according to local standard of care

          -  Prior therapy with an anti-PD-1 or anti-PD1-L1 or -L2 therapy or previously
             participated in a Merck pembrolizumab (MK-3475) trial

          -  Human immunodeficiency virus (HIV)

          -  Hepatitis B or C

          -  Live vaccine within 30 days of planned start of study therapy
      