PDCD1 and head and neck squamous cell carcinoma: Antibodies (Abs) against CTLA-4 (Ipilimumab), PD-1 (Pembrolizumab, Nivolumab, and Cemiplimab), and PD-L1 (Durvalumab, Atezolizumab, and Avelumab) have been approved by the Food and Drug Administration (FDA) to treat patients with advanced melanoma, lymphoma, non-small cell lung cancer (NSCLC), renal cell carcinoma (RCC), bladder cancer, head and neck squamous cell cancer (HNSCC), liver cancer, and Merkel cell carcinoma.