You can participate in this study if you

• Must have given written informed consent (signed and dated).
• Aged 18 years or older at the time of informed consent.
• Recurrent/metastatic histologically or cytologically proven squamous cell carcinoma of the head and neck that is considered incurable by local therapy. Eligible primary tumor locations are oropharynx, oral cavity, hypopharynx, and larynx.
• Presence of measurable tumor per RECIST v1.1 criteria.
• Detectable PD-L1 expression in tumor, defined as CPS ≥20 determined by a Food and Drug Administration-approved test.
• Baseline fresh tumor biopsy or archival specimen.
• ECOG performance status of 0 or 1.
• Adequate organ function within 10 days of study treatment,
• Oxygen saturation on room air ≥92% by pulse oximetry.
• Females must be non-pregnant and non-lactating and either be postmenopausal or agree to adequate birth control.
• Males must be surgically sterile or agree to adequate birth control.
• Has an estimated life expectancy of at least 3 months.
• Has recovered from all complications or surgery and all toxicities of prior therapy

You cannot participate in this study if you

• Prior therapy for metastatic HNSCC.
• Has disease suitable for local therapy with curative intent.
• Primary tumor of the nasopharynx.
• Has received prior therapy with an anti-programmed death 1 (PD-1), anti PD L1, or anti-programmed death-ligand-2 (PD-L2).
• Radiation therapy (or other non-systemic therapy) within 2 weeks of Day 1 of study treatment.
• Known autoimmune disease that has required systemic treatment
• Known immunodeficiency or receiving systemic steroid therapy that would be the equivalent of >10 mg prednisone daily
• Prior allogeneic tissue/solid organ transplant.
• Has significant cardiovascular disease
• Has received a live vaccine within 30 days
• Active infection requiring systemic antiviral or antimicrobial therapy
• History of (non-infectious) pneumonitis that required steroids or current pneumonitis.
• History of other malignancies
• Active HIV infection except patients who are currently stable on antiretroviral therapy for at least 4 weeks
• Active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection.
• Treated or untreated parenchymal brain metastases or leptomeningeal disease.
• Treatment with another investigational drug, biological agent, or device within 1 month of screening, or 5 half-lives of investigational agent (if known), whichever is longer.