CD274 and head and neck cancer: Following search terms were used - (((((("Head and neck cancer" OR "Head and neck squamous cell cancer" OR " HNSCC" OR "recurrent head and neck cancer" OR"unresectable head and neck cancer" OR "metastatic head and neck cancer")) OR ("Head and Neck Neoplasms"[Mesh])) OR ("head neck neoplasm")) OR ("neck neoplasm")) OR ("head neoplasm")) AND (((Pembrolizumab OR "programmed death receptor-1 blocking antibody" OR "PDL1 blocking antibody" OR "programmed death receptor-1 inhibitor" OR "PDL1 inhibitor" OR "immune check-point inhibitor")) OR ("pembrolizumab" [Supplementary Concept])).