PDCD1 and head and neck squamous cell carcinoma: Immune checkpoint inhibitors (ICIs), such as programmed cell death protein-ligand 1 (PD-L1)/programmed cell death protein 1 (PD-1), can be used in therapies to prolong the outcome of progressive and platinum-refractory HNSCCs [5–10]; however, the objective response rate is low, at approximately 15% of patients with HNSCC [11].