HK2 and cancer: The type II isozyme is highly expressed in tumor cells23, and is thought to be the key enzyme in glucose metabolism and the Warburg effect24, Two steps are required to accumulate FDG in cancer cells: (1) facilitated diffusion through a glucose transport protein (GLUT-1); and (2) subsequent phosphorylation by one of the hexokinase isoforms (HK-II) to form FDG-6-phosphate.