Radiotherapy is a powerful inducer of inflammation, and the expression of Programmed death-ligand 1 (PD-L1) is known to be enhanced by inflammatory cytokines, including interferon-gamma (IFNg). Experimental evidence from mice models have shown that radiotherapy induces increased PD-L1 expression in tumor tissue. Moreover, there is evidence suggesting that HNSCC with T-cell infiltration is more sensitive to radiotherapy. There is thus a strong rationale for combing PD-1 inhibitors with radiotherapy. However, this potential remains largely unexplored in humans. The investigators consider that head-and-neck cancer is a particularly attractive entity for investigating this therapeutic combination, because of i) the high radiosensitivity of this cancer form ii) the clinical efficacy of Programmed cell death protein 1 (PD-1) inhibitors as monotherapy in early clinical trials iii) the availability of tumor biopsies for translational/biomarker research.The RT given in the present study gives considerable side effects, related to inflammation that may be enhanced by Programmed cell death protein 1 (PD-1) blockade.