Tumor cells produce hypoxia-inducible factor (HIF) as an important mediator of tumor metabolism, which regulates the expression of target genes, such as erythropoietin, iron metabolism-related genes, VEGF, GLUT1, glycolytic enzymes, heme oxygenase HO2-1, and inducible nitric oxide synthase. This evidence concerns the gene NOS2 and neoplasm.