ABCG2 and cancer: As Notch is a well-described key player in cancer stem cell regulation, some of the ABCG2-regulated genes (e.g. Hes1) are key Notch downstream target genes, and ABCG2/Notch interplay has been previously described14, 15, we speculated that the stemness-promoting effect of ABCG2 could be mediated by Notch.