Intraductal Papillary Mucinous Neoplasms of the Pancreas
In the past decade, substantial improvements have taken place in our understanding of pancreatic intraductal papillary mucinous neoplasms (IPMNs). Their distinction from their kindred, mucinous cystic neoplasm, has been well established; the latter delineated by the de-novo cyst formation, presence of ovarian type stroma, and related occurrence almost exclusively in perimenopausal females. Characterization of salient features of IPMNs, in particular, the identification of the two biologically and prognostically distinct subsets, branch duct (BD) or main duct (MD), has allowed the development of more focused management protocols. For BD, most examples of which are ''incidentalomas'', it is now widely accepted that watchful waiting is a highly valid consideration provided that they are small (< 3cm), non-complex, and show no signs of transformation, because these typically prove to be low-grade dysplastic (previously called adenoma), and exhibit the innocuous gastric phenotype. The MD type, on the other hand, is often associated with chronic pancreatitis, is mostly of intestinal phenotype (occasionally of oncocytic or pancreatobiliary phenotype), typically proves to have at least moderate-grade and often high-grade dysplasia, and thus it is believed that they warrant surgical intervention if feasible. Application of surgery and its extent, however, needs to be weighed against the often old age of the patients, existing comorbidities, and frequent occurence of synchronous malignancies that IPMNs patients notorious for. It has now been well recognized that IPMNs represent an ''adenoma-carcinoma'' sequence; while non-invasive examples are often cured, invasive cases have a variably malignant course. Colloid (muconodular) type invasion typically arise from the intestinal type IPMNs (MUC2/CDX2 expressing intestinal pathway of carcinogenesis), and tend to have protracted clinical course despite their large size. In contrast, ductal (tubular) invasion, thus far seems to be very similar to ordinary pancreatic adenocarcinoma arising from PanIN, both at morphologic, molecular and prognostic aspects. Further studies are needed to establish more targeted management protocols for these tumors as well as to determine the carcinogenetic pathways involved in this challenging tumor type, which may then provide new perspectives to the carcinogenesis at large.
Copyright © 2010 Elsevier Ltd. All rights reserved.
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