Cytokeratin 20 is a 46-kDa intermediate filament protein that interacts predominantly with Merkel cells, urothelium, and gastric and intestinal epithelium. Under normal, hyperplastic, and neoplastic circumstances, anti-Cytokeratin 20 is helpful in identifying particular types of these epithelial cells.3 Cytokeratin 20 has been discovered in a variety of adenocarcinomas, including those of the colon and stomach. There has been reactivity in Merkel cell carcinomas. Breast tumors, in contrast, are usually non-reactive.