GSTP1 and head and neck squamous cell carcinoma: However, the high expression levels of the remaining six genes were closely related to the unfavorable prognosis of HNSCC patients (EGFR: P = 0.014; GSTM1: P = 0.004; GSTP1: P = 0.034; IL1B: P = 0.03; NOS3: P = 0.039 and TP53: P = 0.02; Figure 5).