PDCD1 and head and neck squamous cell carcinoma: In 2016, backed by the results of two landmark trials KEYNOTE-012 (NCT01848834) and CheckMate 141 (NCT02105636) – the anti-PD-1 monoclonal antibodies pembrolizumab and nivolumab became the first immunotherapies to gain FDA approval for the treatment of patients with R/M HNSCC [14, 42–44].