DKK1 and esophageal cancer: Components of this pathway, including Wnt ligands (e.g., Wnt1, Wnt2B, Wnt3, Wnt5A, Wnt7B, and Wnt10A), Frizzled receptors (such as FZD2, FZD7, FZD8, and FZD9), downstream effectors such as β-catenin and TCF/LEF transcription factors, and inhibitors such as DKK1, are increasingly recognized as promising diagnostic and prognostic biomarkers in colorectal, gastric, pancreatic, and esophageal cancers.