PDCD1 and head and neck squamous cell carcinoma: The use of anti-PD-1/PD-L1 mAb has been shown to restore T-cell-mediated antitumour immunity—FDA-approved pembrolizumab and nivolumab in 2016 for patients with recurrent, metastatic, and unresectable HNSCC [8,19,22,36,39].