In its turn, the Wnt/β-catenin signaling pathway, hyperactivated in CSCs, was shown to upregulate the expression of CD44, CD133 or Prominin 1 (PROM1), leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), aldehyde dehydrogenase (ALDH), and the membrane transporters ABCB4 and ABCG2 (all are phenotypic markers of cancer cell stemness) (Figure 1; [1,2,3,4,5,9]). This evidence concerns the gene ABCG2 and cancer.