Cytokeratin 20 is a type I keratin which is primarily expressed in gastric and intestinal epithelium, urothelium, and Merkel-cells. The keratins are intermediate filament proteins responsible for the structural integrity of epithelial cells and are subdivided into cytokeratins and hair keratins. The type I cytokeratins consist of acidic proteins which are arranged in pairs of heterotypic keratin chains. Their genes are clustered in a region of chromosome 17q12-q21. Cytokeratin 20 is a major