Prognostic relevance of pathologic subtypes and minimal invasion in intraductal papillary mucinous neoplasms of the pancreas

Intraductal papillary mucinous neoplasms (IPMNs) of the pancreas are classified into the following four histopathologic subtypes: gastric, intestinal, pancreatobiliary, and oncocytic. However, the clinicopatholgic characteristics of IPMN subtypes have not been fully clarified. Recently, a subgroup classification of minimally invasive intraductal papillary mucinous carcinomas (MI-IPMCs) was suggested in contrast to overt invasive carcinoma from IPMCs (IC-IPMCs). The purpose of this study was to determine whether or not the pathologic subtype classification can predict prognosis and to validate the usefulness of the newly proposed diagnostic criteria of MI-IPMCs. We reviewed the clinicopathologic characteristics of 142 surgically resected cases of IPMNs. There were 54, 56, 30, and two cases of the gastric, intestinal, pancreatobiliary, and oncocytic types of IPMNs, respectively. The intestinal and pancreatobiliary types were more likely to have a main duct type. All gastric type tumors were adenomas or moderate dysplasia, whereas greater than one half of the intestinal and pancreatobiliary types were carcinomas in situ or invasive carcinomas. A significant difference in recurrence and death rate was noted for invasive carcinoma between the intestinal and pancreatobiliary types. The majority of MI-IPMCs were the intestinal type, whereas the majority of IC-IPMCs were the pancreatobiliary type. The IC-IPMC group showed a decreased recurrence-free and overall survival with statistically significance (p < 0.001 and p = 0.001, respectively). Our results suggest that the pathologic subtype classification and the newly proposed diagnostic criteria for minimal invasion may also be useful to predict prognosis of IPMNs of the pancreas.