Malignant, but not benign, intraductal papillary mucinous neoplasm preferentially associates with prior extrapancreatic malignancies.

Intraductal papillary mucinous neoplasm (IPMN) has been associated with a high incidence of extrapancreatic malignancies (EPMs). However, it is controversial whether IPMN is prognostic for EPM. We aimed to help clarify the issue studying this association in patients with histologically proven IPMN. We reviewed 51 surgically resected IPMNs in Saitama Medical Center, Jichi Medical University between January 1991 and June 2012. Mean follow-up was 63.7±47.8 months. The observed EPM incidence was compared with the expected incidence of cancer in Japan. Of the 51 IPMNs, 14 were malignant and the rest benign. Seventeen EPMs developed in 15 patients (29.4%), nine of which occurred prior to IPMN diagnosis. For all IPMNs, the standardized incidence ratio (SIR) was significantly increased for the six types of reported EPMs (SIR=2.18, CI=1.31-3.42, P=0.004). Benign IPMNs showed no association with EPMs (SIR=0.92, CI=0.43-1,76, P=0.87). In contrast, malignant IPMNs showed a higher association (SIR=3.83, CI=1.87-7.03, P=0.0009). However, the association was mostly due to the prior EPMs, as removal of metachronous EPMs had no significant effect (SIR=3.63, CI=1.59-7.17, P=0.005). Thus, only malignant IPMNs drive the significant association with prior EPMs, showing a near 4-fold increased incidence compared to the general Japanese population. Histological characterization of IPMNs may offer clinical value for EPM patient management. We hypothesize that these observations may be explained if some patients with EPMs present a higher risk to develop IPMNs (and vice versa), possibly resulting from an uncharacterized multiple cancer predisposition condition.