NANOG and neoplasm: Since a gradient of oxygen concentration is present between the blood vessels, which have a relatively high oxygen concentration, and the foci of ischemic necrosis, which are under intense hypoxia (Fig 7), the zone containing SOX2+ (or NANOG+) HIF-1α+ RNApII-S2P-/low cells may be under an appropriate degree of hypoxia for maintaining the expression of HIF-1α protein at a moderate level, which would maintain the tumor cells under a quiescent state and support a higher tumorigenic potential.