PDCD1 and head and neck squamous cell carcinoma: Considering the intratumor heterogeneity of PD-L1 expression (126), the sensitivity of the evaluation system (127, 128), the influence of factors such as specimens of different sources (27) on the expression of PD-L1, and that the expression pattern of specific immune checkpoint in HNSCC patients may also promote the development and efficacy of immunotherapy (129), all these urge us to pay attention to the importance of the expression pattern of PD-1/PD-L1 rather than to singly explore the expression level of PD-1/PD-L1.