PDCD1 and head and neck cancer: Programmed cell death 1 ligand 1(PD-L1) is highly expressed in many tumors, and monoclonal antibodies (mAb) to the programmed cell death 1/programmed cell death 1 ligand 1(PD-1/PD-L1) pathway have achieved good results in the treatment of malignant melanoma, non-small cell lung cancer, urothelial cancer and head and neck cancer [2], so PD-L1 is a good therapeutic target.