Mesothelin Expression in Pancreatic Mucinous Cysts

Objectives: Mesothelin (MSLN) is a differentiation antigen found to be overexpressed in intraductal papillary mucinous neoplasms (IPMNs) and is a potential treatment target in pancreatic ductal adenocarcinoma. Methods: From institutional archives, 114 cases of resected pancreatic mucinous cysts were identified, including IPMN and mucinous cystic neoplasm (MCN). Immunohistochemical analysis of MSLN was performed on representative sections. Results: MSLN was seen more frequently in neoplastic epithelial cells from IPMN (39/52; P < .0005) and MCN (9/14; P < .0001) compared with unremarkable adjacent pancreatic and bile ducts (0/57) and benign foveolar and duodenal epithelium (0/21). When present, MSLN was diffusely expressed in neoplastic epithelium and only focally expressed in adjacent ducts (8/57). No significant difference was seen (P = .26) in MLSN expression between IPMN (79%) and MCN (83%) when only presence or absence was considered. Conclusion: Our findings suggest that MLSN can be used as a marker of neoplastic transformation of epithelial cells in pancreatic mucinous cysts. The findings can help identify neoplastic mucinous epithelium.