PDCD1 and head and neck squamous cell carcinoma: Pembrolizumab is a high-affinity, humanised, IgG4-κ monoclonal antibody targeting PD-1 that was first approved by the FDA in 2017 according to the results of the phase Ib KEYNOTE 012 cohort amplification trial.64 In 2019, a phase III clinical study using pembrolizumab (KEYNOTE 048) in the treatment of relapsed or metastatic HNSCC reported superior treatment results from pembrolizumab.