Invasive pancreatic ductal adenocarcinoma is an almost uniformly fatal disease. Several distinct noninvasive precursor lesions can give rise to invasive adenocarcinoma of the pancreas, and the prevention, detection, and treatment of these noninvasive lesions offers the potential to cure early pancreatic cancers. Noninvasive precursors of invasive ductal adenocarcinoma of the pancreas include pancreatic intraepithelial neoplasias (PanINs), intraductal papillary mucinous neoplasms (IPMNs), and mucinous cystic neoplasms. Diagnostic criteria, including a distinct ovarian-type stroma, and a consistent nomenclature are well established for mucinous cystic neoplasms. By contrast, consistent nomenclatures and diagnostic criteria have been more difficult to establish for PanINs and IPMNs. Because both PanINs and IPMNs consist of intraductal neoplastic proliferations of columnar, mucin-containing cells with a variable degree of papilla formation, the distinction between these two classes of precursor lesions remains problematic. Thus, considerable ambiguities still exist in the classification of noninvasive neoplasms in the pancreatic ducts. A meeting of international experts on precursor lesions of pancreatic cancer was held at The Johns Hopkins Hospital from August 18 to 19, 2003. The purpose of this meeting was to define an international acceptable set of diagnostic criteria for PanINs and IPMNs and to address a number of ambiguities that exist in the previously reported classification systems for these neoplasms. We present a consensus classification of the precursor lesions in the pancreatic ducts, PanINs and IPMNs.

International experts met to discuss recent advances and to revise the 2004 recommendations for assessing and reporting precursor lesions to invasive carcinomas of the pancreas, including pancreatic intraepithelial neoplasia (PanIN), intraductal papillary mucinous neoplasm (IPMN), mucinous cystic neoplasm, and other lesions. Consensus recommendations include the following: (1) To improve concordance and to align with practical consequences, a 2-tiered system (low vs. high grade) is proposed for all precursor lesions, with the provision that the current PanIN-2 and neoplasms with intermediate-grade dysplasia now be categorized as low grade. Thus, “high-grade dysplasia” is to be reserved for only the uppermost end of the spectrum (“carcinoma in situ”–type lesions). (2) Current data indicate that PanIN of any grade at a margin of a resected pancreas with invasive carcinoma does not have prognostic implications; the clinical significance of dysplasia at a margin in a resected pancreas with IPMN lacking invasive carcinoma remains to be determined. (3) Intraductal lesions 0.5 to 1 cm can be either large PanINs or small IPMNs. The term “incipient IPMN” should be reserved for lesions in this size with intestinal or oncocytic papillae or GNAS mutations. (4) Measurement of the distance between an IPMN and invasive carcinoma and sampling of intervening tissue are recommended to assess concomitant versus associated status. Conceptually, concomitant invasive carcinoma (in contrast with the “associated” group) ought to be genetically distinct from an IPMN elsewhere in the gland. (5) “Intraductal spread of invasive carcinoma” (aka, “colonization”) is recommended to describe lesions of invasive carcinoma invading back into and extending along the ductal system, which may morphologically mimic high-grade PanIN or even IPMN. (6) “Simple mucinous cyst” is recommended to describe cysts >1 cm having gastric-type flat mucinous lining at most minimal atypia without ovarian-type stroma to distinguish them from IPMN. (7) Human lesions resembling the acinar to ductal metaplasia and atypical flat lesions of genetically engineered mouse models exist and may reflect an alternate pathway of carcinogenesis; however, their biological significance requires further study. These revised recommendations are expected to improve our management and understanding of precursor lesions in the pancreas.

Intraductal papillary mucinous neoplasm (IPMN) is a common pancreatic cystic neoplasm that is often invasive and metastatic, resulting in a poor prognosis. Few molecular alterations unique to IPMN are known. We performed whole-exome sequencing for a primary IPMN tissue, which uncovered somatic mutations in KCNF1, DYNC1H1, PGCP, STAB1, PTPRM, PRPF8, RNASE3, SPHKAP, MLXIPL, VPS13C, PRCC, GNAS, KRAS, RBM10, RNF43, DOCK2, and CENPF. We further analyzed GNAS mutations in archival cases of 118 IPMNs and 32 pancreatic ductal adenocarcinomas (PDAs), which revealed that 48 (40.7%) of the 118 IPMNs but none of the 32 PDAs harbored GNAS mutations. G-protein alpha-subunit encoded by GNAS and its downstream targets, phosphorylated substrates of protein kinase A, were evidently expressed in IPMN; the latter was associated with neoplastic grade. These results indicate that GNAS mutations are common and specific for IPMN, and activation of G-protein signaling appears to play a pivotal role in IPMN.

Several diverse genetically engineered mouse models of pancreatic exocrine neoplasia have been developed. These mouse models have a spectrum of pathologic changes; however, until now, there has been no uniform nomenclature to characterize these changes. An international workshop, sponsored by The National Cancer Institute and the University of Pennsylvania, was held from December 1 to 3, 2004 with the goal of establishing an internationally accepted uniform nomenclature for the pathology of genetically engineered mouse models of pancreatic exocrine neoplasia. The pancreatic pathology in 12 existing mouse models of pancreatic neoplasia was reviewed at this workshop, and a standardized nomenclature with definitions and associated images was developed. It is our intention that this nomenclature will standardize the reporting of genetically engineered mouse models of pancreatic exocrine neoplasia, that it will facilitate comparisons between genetically engineered mouse models and human pancreatic disease, and that it will be broad enough to accommodate newly emerging mouse models of pancreatic neoplasia. (Cancer Res 2006; 66(1): 95-106)

Objective: The clinicopathological significance of four morphological types of intraductal papillary mucinous neoplasms of the pancreas (IPMNs; gastric, intestinal, pancreatobiliary and oncocytic) was assessed. Design: Retrospective multicentre analysis of 283 surgically resected IPMNs. Results: Of the 283 IPMNs, 139 were of the gastric type, 101 were intestinal, 19 were pancreatobiliary and 24 were oncocytic. These types were significantly associated with clinicopathological factors including sex (p=0.0032), age (p=0.00924), ectatic duct size (p=0.0245), detection of mural nodules (p=4.09×10 ⁻⁶ ), histological grade (p<2.20×10 ⁻¹⁶ ), macroscopic types with differential involvement of the pancreatic duct system (p=3.91×10 ⁻⁵ ), invasive phenotypes (p=3.34×10 ⁻¹² ), stage (p<2.20×10 ⁻¹⁶ ) and recurrence (p=0.00574). Kaplan–Meier analysis showed significant differences in patient survival by morphological type (p=5.24×10 ⁻⁶ ). Survival rates at 5 and 10 years, respectively, were 0.937 (95% CI 0.892 to 0.984) for patients with gastric-type IPMNs; 0.886 (95% CI 0.813 to 0.965) and 0.685 (95% CI 0.553 to 0.849) for those with intestinal-type IPMNs; 0.839 (95% CI 0.684 to 1.000) and 0.734 (95% CI 0.526 to 1.000) for those with oncocytic-type IPMNs; and 0.520 (95% CI 0.298 to 0.909) and undetermined for those with pancreatobiliary-type IPMNs. Analysis by the Cox proportional hazards model comparing prognostic risks determined by stage and the morphological and macroscopic types indicated that staging was the most significant predictor of survival (p=3.68×10 ⁻⁸ ) followed by the morphological type (p=0.0435). Furthermore, the morphological type remained a significant predictor in a subcohort of invasive cases (p=0.0089). Conclusion: In this multicentre retrospective analysis, the morphological type of IPMN appears to be an independent predictor of patient prognosis.