For example, tumor cells produce hypoxia-inducible factor (HIF), which is an important mediator of tumor metabolism and can regulate the expression of target genes such as VEGF, glycolytic enzymes, erythropoietin, iron metabolism-related genes, glucose transporter-1(GLUT1), heme oxygenase HO2-1, inducible nitric oxide synthase, etc. (67–69). The gene discussed is EPO; the disease is neoplasm.