Cytokeratin 18 is an acidic keratin which is found primarily in non squamous epithelia and is present in a majority of adenocarcinomas and ductal carcinomas but not in squamous cell carcinomas. Cytokeratin 18 exists in combination with Cytokeratin 8, a basic keratin. Hepatocellular carcinomas have been reportedly defined by the use of antibodies that recognize only Cytokeratins 8 and 18.