PDCD1 and head and neck squamous cell carcinoma: Due to the immune suppressive function similar to PD-1 and PD-L1, LAG-3 overexpression on tumor tissue has been reported to be associated with unfavorable clinical parameters and poor prognosis in various types of cancer, such as melanoma (24), head and neck squamous cell carcinoma (21), non-small cell lung cancer (NSCLC) (26), diffuse large B- cell lymphoma (33) and so on.