Quad Shot Radiotherapy in Combination With Immune Checkpoint Inhibition

Inclusion Criteria: * Advanced, recurrent or metastatic head and neck squamous cell carcinoma, as defined by clinical or pathological diagnosis of any of the following: * Locally advanced head and neck squamous cell carcinoma not suitable for curative local treatment. * Locally recurrent head and neck squamous cell carcinoma not suitable for curative local treatment within or outside a previously irradiated tissue. * Metastatic head and neck squamous cell carcinoma. * Target site in the head and neck region amenable to quad-shot palliative radiotherapy, for which palliative radiotherapy is recommended, as determined by the treating radiation oncologist. * Age 18 years or greater at time of registration. * ECOG Performance Status of 0-2. * Women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately. * Ability to understand and the willingness to sign an IRB-approved informed consent document (either directly or via a legally authorized representative). * Willingness to provide blood and saliva samples for exploratory research purposes. * Organ and Marrow Function as defined below: Absolute neutrophil count (ANC) ≥ 1.5 x 109/L, platelet count ≥ 100 x 109/L, hemoglobin ≥ 9.0 g/dL, serum bili…