Histological subclassification and its clinical significance

Intraductal papillary mucinous neoplasms (IPMNs) show variations in morphological and immunohistochemical features of cells and papillae. Based on the variations, IPMNs are classified into four distinct subtypes, namely, gastric type, intestinal type, pancreatobiliary type, and oncocytic type. These subtypes are well associated with clinicopathological features and known to be an independent prognostic factor. The gastric-type IPMNs show thick fingerlike papillae consisted of low-grade dysplastic cells expressing MUC5AC and occasionally MUC6. Patients with the gastric-type IPMN usually show fair prognosis. However, some of the gastric-type IPMNs are associated with invasive carcinoma that leads to poor prognosis. The intestinal-type IPMNs show villous papillae consisted of high-grade dysplastic cells expressing MUC2 and MUC5AC. They are often associated with mucinous colloid carcinoma. The prognosis is less favorable, around 90 % and 70 % in the 5- and 10-year survivals. The pancreatobiliary-type IPMNs show complex fernlike papillae consisted of high-grade dysplastic cells expressing MUC1 and MUC5AC. They are often associated with tubular adenocarcinoma and, hence, the prognosis is very poor, around 50 % and none in the 5- and 10-year survivals. The oncocytic-type IPMN show fractal-shaped papillae consisted of high-grade oncocytic cells expressing MUC5AC and MUC6. They are occasionally associated with oncocytic carcinoma. Prognosis is less favorable, around 80 % and 70 % in the 5- and 10-year survivals. These subtypes of IPMN can be determined not only on surgical specimen but also on cytology or biopsy specimen; hence, information of the subtypes is available during diagnostic process as well as postoperative follow-up, which is expected to facilitate better clinical management of patients with IPMN.