MUC1 and pancreatic intraductal papillary-mucinous neoplasm: The level of MUC-1 expression in pancreatobiliary- and oncocytic-type IPMNs, as detected by immunohistochemistry, is thought to be very low (5,15); therefore, it is expected to be fairly difficult to determine the histological type of IPMN based on the immunohistochemical expression of MUC-1.