Cytokeratin 18 (CK18) is present in simple, glandular, and transitional epithelial cells, but is absent in stratified epithelial cells. CK18 usually multimerizes with Cytokeratin 8, and Anti-Cytokeratin 18 is useful for detecting adenocarcinomas of simple and glandular epithelium origin, as well as poorly differentiated squamous carcinoma cells.