POU5F1 and cancer: Hypoxia as a physiological phenomenon exists in tumors.33,34 Although a few studies have paid attention to the influence of hypoxia on unsorted cancer cells,15,16,35,36 these studies could not identify the role of hypoxia on non-CSCs, because the increased expression of CD133, SOX-2 or OCT-4 under hypoxia may be from CSCs themselves.