CD274 and head and neck squamous cell carcinoma: CTLA-4 inhibitors (Ipilimumab) and PD-1/PD-L1 inhibitors (Nivolumab, Pembrolizumab, Atezolizumab, Durvalumab, among others) are the two main categories of ICIs out of which Nivolumab and Pembrolizumab (both PD-1 inhibitors) have been approved for the treatment of recurrent/metastatic HNSCC.