PDCD1 and head and neck squamous cell carcinoma: These agents include the cytotoxic T lymphocyte-associated protein 4 (CTLA4)-specific mAb ipilimumab (Yervoy), which is licensed for the treatment of melanoma [2–4]; two mAbs targeting programmed cell death 1 (PCDC1; best known as PD-1), namely nivolumab (Opdivo) and pembrolizumab (Keytruda), which are approved for use in patients with melanoma, head and neck squamous cell carcinoma, non-small cell lung carcinoma (NSCLC) and Hodgkin's lymphoma [5–14]; and atezolizumab (Tecentriq), a mAb targeting CD274 (best known as PD-L1) recently approved for use in bladder carcinoma patients [15, 16].