Novel insights into immunohistochemical analysis for diagnosing serous neoplasm of the pancreas: aquaporin 1, stereocilin, and transmembrane protein 255B

Aims Serous (cystic) neoplasm (SCN) of the pancreas is generally benign, and surgical treatment is recommended in only a limited number of cases. To avoid unnecessary surgery, an accurate diagnosis of SCN is essential. In the present study, we aimed to identify new immunohistochemical markers with which to distinguish SCN from other tumours. Methods and results We compared the comprehensive gene expression profiles of SCN with those of normal pancreas and pancreatic ductal adenocarcinoma (PDAC). We selected the candidate molecules that were up‐regulated in SCN, were minimally expressed or unexpressed in PDAC, and had specific and available antibodies suitable for immunohistochemistry, and then analysed their immunohistochemical expression in various tumours. We selected aquaporin 1 (AQP1), stereocilin (STRC), fibroblast growth factor receptor 3 (FGFR3), and transmembrane protein 255B (TMEM255B), which were diffusely expressed in SCN cells in 79%, 100%, 100% and 100% of SCN cases. AQP1 was not expressed in other tumours, except in 20% of mucinous cystic neoplasms (MCNs) and 19% of PDACs. STRC was rarely expressed in MCNs, neuroendocrine neoplasms (NENs), and PDACs. FGFR3 was expressed in 31% of intraductal papillary mucinous neoplasms (IPMNs), 50% of intraductal oncocytic papillary neoplasms, 40% of NENs, 30% of acinar cell carcinomas, 40% of solid pseudopapillary neoplasms, and 52% of PDACs. TMEM255B was not expressed in the other tumours, except in 50% of MCNs, 80% of gastric‐subtype IPMNs, and 29% of PDACs. All antigens were usually expressed in a small proportion of cells when they were positive in tumours other than SCN. Conclusions These findings indicate that AQP1 and STRC, and potentially TMEM255B, may act as SCN markers.