DKK2 and esophageal cancer: MiR-221 was overexpressed in 5-FU resistant esophageal cancer cells and EAC tissue and could potentiate 5-FU resistance by directly down-regulating the expression of dickkopf Wnt signaling pathway inhibitor 2 (DKK2) and activating the Wnt/β-catenin-EMT pathways (Wang Y. et al., 2016).