PDCD1 and head and neck carcinoma: PD-L1 is an immunoinhibitory molecule, which induces T-cell-mediated immune tolerance by activating PD-1 located on the surface of T cells.[21] Thus, a significant antitumor effect has been shown by immune therapies that target the PD-1/PD-L1 axis in certain types of solid tumors, including melanoma, non-small cell lung cancer (NSCLC), head and neck carcinomas and so on.