PDCD1 and head and neck squamous cell carcinoma: Nivolumab and Pembrolizumab, both IgG4 anti-PD-1 monoclonal antibodies, were evaluated in phase III trials in R/M HNSCC patients with oral cavity, oropharynx, larynx, or hypopharynx primary after failure of platinum-based chemotherapy, and compared to investigator choice chemotherapy (Docetaxel, Cetuximab, or Methotrexate).