PDCD1 and head and neck squamous cell carcinoma: Although the introduction of monoclonal antibodies against PD-1 such as pembrolizumab has revolutionized the therapy against many cancer forms, including HNSCC (8), and it is now being used as a first-line agent against R/M HNSCC after positive results from the KEYNOTE-048 study (11), only a fraction of patients show long-term response under this treatment (44, 45).