CTLA4 and head and neck squamous cell carcinoma: Except for surgery, radiotherapy, chemotherapy, and targeted therapy based on molecular subtypes and the TNM stage of HNSCC, immunotherapy is an emerging treatment modality due to the promising therapeutic effect of selective immune checkpoint inhibitors (ICI), including monoclonal antibodies against programmed death 1 (PD-1), programmed death-ligand 1 (PD-L1) and cytotoxic T lymphocyte-associated protein-4 axes (CTLA-4) 3-5.