KEGG analysis revealed that Cluster1 ESCC samples upregulated pathways controlling GnRH secretion, phototransduction, TCA cycle, cAMP signaling pathway and aldosterone synthesis and secretions, while cluster2 ESCC samples were enriched in pathways related to olfactory transduction, cytokine–cytokine receptor interaction and ABC transporters (Fig. 5C). This evidence concerns the gene ABCG2 and esophageal squamous cell carcinoma.