Analysis of Prognostic Factors and a Proposed New Classification for Invasive Papillary Mucinous Neoplasms

The characteristics of invasive type-intraductal papillary mucinous neoplasm (invasive IPMN) have not been fully explored due to limited reports. Furthermore, a straightforward method is needed to describe its aggressiveness. The purpose of this study was to investigate prognostic factors and to examine the clinical significance of percentage pancreatic volume occupied by the invasive component in invasive IPMN. Of 217 patients who underwent surgical resection with a diagnosis of IPMN between 2001 and 2008, 41 had invasive IPMC. We serially sectioned pancreatic parenchyma at 5-7-mm intervals. Whole slides were reviewed by a pancreas-biliary tract special pathologist, who determined the percentage pancreatic volumes occupied by the invasive components (IC%) in whole IPMN lesions. By multivariate analysis, perineural invasion, metastasis, AJCC stage, and invasive component percentage (IC%) significantly predicted prognosis. IC% was found to be significantly associated with survival. Patients with an IC% < 10 had a 3-year survival rate (YSR) of 100%, whereas patients with an IC% > 50% had a 3 YSR of 36.5% and those with an IC% of 10-50% had a 3 YSR of 71.4% (p = 0.041). In addition to conventional prognostic factors, such as AJCC stage and perineural invasion, the percentage of pancreatic volume occupied by the invasive component (IC%) appears to be an important prognostic factor in invasive IPMN. The concept of IC% is straightforward, semiquantitative, and objective, and offers a means of determining tumor aggressiveness; hence, it could be a means of classifying invasive IPMN.