PDCD1 and head and neck cancer: Immune checkpoint inhibitors, such as those targeting cytotoxic T lymphocyte-associated-4 (CTLA-4) and programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1), have recently been developed (4) and tested, both alone and in combination with other targeted therapy, chemotherapy, or radiotherapy in various malignancies, including lung cancer, melanoma, head and neck cancer, genitourinary cancer, and lymphoma (5).