PDCD1 and head and neck cancer: In recent years, various PD-1(Programmed cell death protein 1)/PD-L1(Programmed death-ligand 1) antibodies, including pembrolizumab, nivolumab, avelumab, durvalumab, and atezolizumab, have gained FDA(Food and Drug Administration) approval for treating melanoma, head and neck cancer, lymphoma, urothelial cancer, breast cancer, lung cancer, and renal cell carcinoma (2, 3).