In addition, although PROM1 (CD133) is a Wnt-target gene [87] and HIFαs appear to display a counterbalancing function on β-catenin/TCF transcriptional activity in response to oxygen levels [141, 142], it is unclear how the balance between HIF1α and HIF2α during hypoxia contribute to Wnt pathway and CD133 regulation mostly in cancer cells where Wnt pathway plays a crucial role. This evidence concerns the gene HIF1A and cancer.