Keratins are cytoplasmic intermediate filament proteins expressed by epithelial cells. Cytokeratin 18 is a type I keratin. This antibody reacts with cytokeratin 18 in glandular epithelial cells of the digestive, respiratory, and urogenital tracts, endocrine and exocrine cells as well as mesothelial cells;it does not react with stratified squamous epithelia. It detects epithelial tumors of the gastrointestinal tract, lung, breast, pancreas, ovary, and thyroid; adenocarcinomas originating from them and squamous carcinomas.