GSTM1 and head and neck squamous cell carcinoma: Furthermore, the correlation between GSTM1 and genes involved in ‘metabolism of xenobiotics by cytochrome p450’ was analyzed, showing that GSTM1 is highly correlated with CYP3A5, CYP2C8 and AKR1C4 (Spearman value ≥ 0.6) and moderately associated with ADH1C, AKR1C3, GSTM2, GSTM5, UGT1A1, UGT1A3, UGT1A5, UGT1A6, UGT1A9 and UGT2A3 in BAA HNSCC (0.4 < Spearman value < 0.6) (Fig. 6C).