HIF1A and neoplasm: Intermittent hypoxia (7% O2, 1 h hypoxia, 30 min reoxygenation, 3 cycles), but not hypoxia without H–R cycles (7% O2, 3 h hypoxia) has been reported to exert HIF-1α dependent radioresistance in TLT-liver carcinoma xenograft models by inhibiting apoptosis in vascular as well as tumor cell compartments thus, resulted into increased tumor regrowth after irradiation.