Cytokeratin 5/6 immunostaining in hepatobiliary and pancreatic neoplasms

Immunohistochemistry with different cytokeratin subsets has been successfully used in the differential diagnosis of various human epithelial neoplasms. Cytokeratin 5/6 antibody, which recently became commercially available, has been found useful in the diagnosis of mesothelioma. Studies have reported only infrequent staining in adenocarcinomas. We investigated the pattern of immunoreactivity for cytokeratin 5/6 in hepatobiliary and pancreatic tumors to determine its diagnostic utility in the morphologic evaluation of these neoplasms. Formalin-fixed. paraffin-embedded tissue sections from 10 hepatocellular carcinomas, seven hepatocellular adenomas, 10 cholangiocarcinomas, 10 pancreatic ductal adenocarcinomas, and 13 pancreatic neuroendocrine carcinomas were immunostained with anticytokeratin 5/6 after heat-induced antigen retrieval utilizing a modified avidin-biotin complex technique. Positive and negative controls stained appropriately. Two pathologists evaluated the slides. Strong but focal cytoplasmic immunoreactivity was observed in five of 10 pancreatic ductal adenocarcinomas and two of 10 cholangiocarcinomas. No immunoreactivity was identified in any cases of hepatocellular carcinoma (0/10), hepatocellular adenoma (0/7), or pancreatic neuroendocrine carcinoma (0/13). Additionally, occasional cytokeratin 5/6 immunoreactive benign ductal epithelial cells were seen in the background in some cases. Fifty percent of pancreatic ductal adenocarcinomas and 20% of cholangiocarcinomas are positive with anti-cytokeratin 5/6 immunostaining. For the evaluation of poorly differentiated neoplasms in the liver, immunoreactivity with cytokeratin 5/6 may help to exclude the possibility of hepatocellular carcinoma. Cytokeratin 5/6 may be helpful as a component in the panel of immunostains to differentiate between poorly differentiated neoplasms.