PDCD1 and head and neck squamous cell carcinoma: The results illustrated that LAG3 (p < 3.35e−05), PDCD1 (p < 1.06e−04), CTLA4 (p < 2.55e−03), HAVCR2 (p < 1.72e−03), TIGIT (p < 1.22e−03), and SIGLEC15 (p < 9.39e−02) were upregulated in WHO grade III compared with WHO grade II of HNSCC (Fig. 6B).