Pembrolizumab (MK-3475) Versus Standard Treatment for Recurrent or Metastatic Head and Neck Cancer (MK-3475-040/KEYNOTE-040)

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