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. Author manuscript; available in PMC: 2015 May 23.
Published in final edited form as: Radiat Res. 2015 May 4;183(5):487–496. doi: 10.1667/RR13959.1

Fig. 2.

Fig. 2

Mechanisms of radioresistance at different pO2. Under the radiobiological or severe hypoxia (pO2 < 3 mmHg), the oxygen fixation hypothesis (OFH) is likely the main mechanism of radioresistance even though expression of DNA repair genes is strongly reduced. In contrast, hypoxia-activated pathways, both HIF-dependent and independent, will be actively operative under the pathological hypoxia (pO2 = 3–15 mmHg) to elicit a multitude of molecular and cellular changes. Chief among them, the cancer stem cell (CSC) phenotype has the potential to play a prominent role in conferring radioresistance.