A Study of Pembrolizumab in Combination With Chemotherapy for Head and Neck Cancer

Inclusion Criteria: * Have clinically confirmed head and neck cancer that is recurrent (comes back/returns to the body) or metastatic (spreads to other parts of the body). * Participants should not have had prior systemic therapy administered in the recurrent or metastatic setting. Systemic therapy which was completed more than 3 months prior to signing consent if given as part of multimodal treatment for locally advanced disease is allowed. * Greater than or equal to 18 years old. * Eastern Cooperative Oncology Group performance status of 0 or 1. * Have measurable disease based on RECIST 1.1 as determined by the site. Tumor lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions. * Participants must have normal organ and marrow function as defined by clinical lab values. * Participants must have provided tissue for programmed cell death ligand 1 (PD-L1) biomarker analysis from a core or excisional biopsy (fine needle aspirate is not adequate). Repeat samples may be required if adequate tissue is not provided. A newly obtained biopsy (within 90 days prior to start of study treatment) is strongly preferred, but an archival sample is acceptable. * Measurable disease (either primary site and/or nodal disease) as assessed by Response Evaluation Criteria in Solid Tumors (RECIST 1.1). * Participants must sign a study-specific informed consent form prior to study entry. Participants should have the ability to u…