KEGG pathway analysis indicates that the differential metabolites in the four types are primarily associated with ABC transporters, Pyrimidine metabolism, D‐Amino acid metabolism, Central carbon metabolism in cancer, Alanine, aspartate and glutamate metabolism, Protein digestion and absorption, Alcoholism, Glycine, serine and threonine metabolism, Lysine degradation, and so on (Figure 2I). The gene discussed is ABCG2; the disease is cancer.