HK1 and head and neck squamous cell carcinoma: Further analysis for HK1 and HK2 expression in HNSCCs indicated that (i) HK2 expression, but not HK1, is positively correlated with tumor stages and grades (Figures 1C,D); (ii) HK2 level, but not HK1, is upregulated in HPV− HNSCC tissues (Figure 1E); and (iii) HK2 expression, but not HK1, is increased in early metastatic HNSCCs [with one to three axillary lymph nodes (N1)] (Figure 1F).