GSTM1 and head and neck squamous cell carcinoma: Moreover, cluster analysis of gene expression in BAA HNSCC revealed that SALL3, C6orf15, NELL1 and GSTM1 are in the same cluster and there was a strong co-expression between SALL3 and GSTM1 genes (Spearman = 0.66, P = 0.00011) (Supplementary Fig. S3).