PDCD1 and head and neck squamous cell carcinoma: Two programmed cell death protein 1 (PD-1) inhibitors, nivolumab and pembrolizumab, are approved for the treatment of patients with recurrent or metastatic HNSCC in the second line (platinum-refractory disease) as well as pembrolizumab alone or in combination with platinum and 5-fluorouracil in the first-line treatment of selected patients.