S100A9 and head and neck squamous cell carcinoma: We found that 2 genes were upregulated (PLAU and SPP1) and 4 genes downregulated (S100A8, S100A9, SPINK5 and ACKR1), which significantly correlated with poor prognosis (p < 0.05) in HNSCC patients (Fig. 4A–F), and we selected these genes for further investigation.