PDCD1 and head and neck squamous cell carcinoma: ICIs that have been subsequently approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA) for the treatment of melanoma, non-small cell lung cancer (NSCLC), renal cell carcinoma (RCC), Hodgkin lymphoma, head and neck squamous cell carcinoma (HNSCC), and urothelial carcinoma include nivolumab and pembrolizumab targeting PD-1, and atezolizumab (for urothelial cancer and NSCLC), avelumab (merkel cell carcinoma and RCC), and durvalumab (NSCLC) targeting PD-L1, as well as ipilimumab targeting CTLA-4 (for melanoma and RCC) [2].