CLDN4 and pancreatic intraductal papillary-mucinous neoplasm: Claudin-4 is highly expressed in pancreaticobiliary ductal PCa (p = 0.015), PanIN, IPMN, MCN, and the major precursor lesions of pancreatic ductal adenocarcinoma (73), and its expression is correlated with the histological tumor grade of IPMN and MCN (11, 23, 34, 57).