Pembrolizumab + Radiation for Locally Adv SCC of the Head and Neck (SCCHN) Not Eligible Cisplatin

This open label, phase II trial will enroll 29 subjects in order to evaluate the efficacy of Pembrolizumab, concomitant with and following standard of care definitive radiation for locally advanced squamous cell carcinoma head and neck patients who are not good candidates for Cisplatin. Objectives include estimating progression free survival and overall survival, response rates, safety and toxicity, and quality of life in these patients. Correlative studies, based on serial blood collections and tumor samples, may be done under a separate protocol based on availability of archival diagnostic tissue.