Further studies revealed a (re-)activation of embryonic programs and/or elevated expression levels of cancer stem cell markers, including forkhead box protein A1 (FOXA1), aldehyde dehydrogenase 1 (ALDH1), ATP-binding cassette sub-family G member 2 (ABCG2), and hepatocyte growth factor receptor (c-Met), in metastatic PDAC cells, suggesting a close relationship between retrograde developmental transition, cancer cell stemness and biological features of metastasis formation [57, 110]. This evidence concerns the gene ABCG2 and cancer.