Upregulation of follistatin and low apoptotic activity in intraductal oncocytic papillary neoplasm of the pancreatobiliary system.

Intraductal oncocytic papillary neoplasm (IOPN) is a rare intraductal tumor of the pancreatobiliary system. Currently, little is known about its distinct characteristics, unlike intraductal papillary mucinous neoplasms (IPMN) and intraductal papillary neoplasms of the bile duct (IPNB). The present study compared 22 IOPNs (18 pancreatic and 4 biliary) with those of 61 IPMNs/8 IPNBs. IOPNs were classified into pure and combined types, depending on the coexistence of IPMN/IPNB. Multiple gene expression analysis (nCounter system) was performed, and hierarchical clustering analysis separated IOPNs(n = 4) and IPMNs(n = 3)/ IPNBs(n = 3), and pathway score analysis supported the result. Volcano plot identified follistatin (FST) as the most upregulated mRNA in IOPN in comparison to the gastric subtype (log2 fold change of 5.34) and the intestinal subtype (that of 5.81) of IPMN/IPNB. The expression of FST in IOPN was also high in quantitative polymerase chain reaction and immunohistochemical analysis. We also found lower apoptotic activity in IOPN, particularly in pure type, compared to high-grade or invasive IPMN/IPNB using immunohistochemistry for cleaved caspase 3. But, combined type IOPN was more similar to IPMN/IPNB than pure IOPN. In conclusion, we proved that IOPN, particularly pure IOPN, is distinct from IPMN/IPNB in FST mRNA overexpression and exhibits lower apoptotic activity.