WIF1 and esophageal squamous cell carcinoma: Genetic and epigenetic alterations, such as DNA hypermethylation in the promoter region of axis inhibition protein 2 (Axin2), adenomatous polyposis coli (APC), Wnt inhibitory factor 1 (WIF-1), and secreted frizzled-related protein (SFRPs), lead to the aberrant activation of Wnt⁄β-catenin signaling pathway in several types of tumors, including ESCC [14].