CLDN4 and in situ carcinoma: In their work on pancreatic cell lines and IPMNs, Tsutsumi and co-workers reported similar findings to those of Lee and co-workers [51] and Tsukahara and co-workers [49], where claudin-4 mRNA expression levels were significantly higher in IPMN borderline neoplasms, carcinoma in situ, and invasive pancreatic carcinoma compared with the expression in IPMN adenomas, in a four-way comparison [50].