Tumors usually exist in a relatively hypoxic microenvironment, which activate HIF in tumor cells, and further activate HIF downstream target genes such as the transporter GLUT1, HK1, HK2, lactate dehydrogenase [167,168], and pyruvate dehydrogenase kinase 1 (PDK1), to ensure the metabolic requirements of the tumor. The gene discussed is HK1; the disease is neoplasm.