Compared with the paired normal group, the relative mRNA levels of PLAU, STC2, TNFRSF4, PDGFA, and DKK1 were significantly higher (p < 0.05) in HNSCC tissues than those in adjacent normal tissues (Figure 9A), the results were very similar to the corresponding expression differences between the 44 matched normal samples and tumor samples in TCGA (Figure 9B), except that the CHGB gene was overexpressed in the validation assay but had relatively low expression in the HNSCC sample of TCGA. Here, DKK1 is linked to head and neck squamous cell carcinoma.