Incidence of Pancreatic Intraepithelial Neoplasia in an Autopsy Series

OBJECTIVES

Pancreatic intraepithelial neoplasia (PanIN) is the currently preferred designation for putative preneoplastic changes in the pancreas. There are few data for the incidence of PanIN in the general population. Our goal was to determine the incidence of PanIN in a large group of pancreases obtained at autopsy.

METHODS

Slides stained with hematoxylin and eosin were scanned to count PanIN.

RESULTS

We found multiple PanINs in most pancreases and at least 1 in 86.4% of 154 pancreases when multiple slides (8-12) from each were examined. The average age at autopsy was 62 years, and 90% of the patients were 40 years or older. Several questions were raised by our observations. Should a minimum size be defined for classification as PanIN? Do PanINs occur in lesions that apparently arise from acinar to ductal metaplasia? Does squamous metaplasia in PanIN have any special significance, and do purely squamous lesions have preneoplastic significance?

CONCLUSIONS

We conclude that the incidence of PanIN is higher than previously reported.

Pancreatic Ductal Adenocarcinoma: Recent Updates

This Guest Editorial introduces this month's special Pancreatic Cancer Theme Issue, a series of reviews intended to highlight the pathologic to molecular profiles and diagnoses of benign and neoplastic pancreatic lesions.

Association of IgG4 response and autoimmune pancreatitis with intraductal papillary-mucinous neoplasms

OBJECTIVES

Concurrent intraductal papillary-mucinous neoplasm (IPMN) and autoimmune pancreatitis (AIP) was observed in a patient (index case) at our institution. Cases of coincidental IPMN and type 1 AIP and concurrent ductal adenocarcinoma (PDAC) and AIP have been previously reported. In this study we evaluate the hypothesis that IPMN elicits an IgG4 response.

METHODS

Twenty-one pancreases (including the index case) with IPMN resected at our institution were studied. H&E stained slides were reviewed and blocks of peritumoral pancreas were immunostained with IgG4 to look for IgG4-positive plasma cells.

RESULTS

We found evidence of variable IgG4 overexpression in 4/21 (19%) of IPMN. These included the index case and three others without stigmata of AIP.

CONCLUSION

A small subset of pancreatic neoplasms including intraductal papillary-mucinous neoplasms (IPMN) is associated with an IgG4 autoimmune response that sometimes progresses to peritumoral type 1 AIP and less often to diffuse AIP and IgG4-related systemic disease.

A Revised Classification System and Recommendations From the Baltimore Consensus Meeting for Neoplastic Precursor Lesions in the Pancreas

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.

The diaphragms of fenestrated endothelia: gatekeepers of vascular permeability and blood composition

Fenestral and stomatal diaphragms are endothelial subcellular structures of unknown function that form on organelles implicated in vascular permeability: fenestrae, transendothelial channels, and caveolae. PV1 protein is required for diaphragm formation in vitro. Here, we report that deletion of the PV1-encoding Plvap gene in mice results in the absence of diaphragms and decreased survival. Loss of diaphragms did not affect the fenestrae and transendothelial channels formation but disrupted the barrier function of fenestrated capillaries, causing a major leak of plasma proteins. This disruption results in early death of animals due to severe noninflammatory protein-losing enteropathy. Deletion of PV1 in endothelium, but not in the hematopoietic compartment, recapitulates the phenotype of global PV1 deletion, whereas endothelial reconstitution of PV1 rescues the phenotype. Taken together, these data provide genetic evidence for the critical role of the diaphragms in fenestrated capillaries in the maintenance of blood composition.

PV1 down-regulation via shRNA inhibits the growth of pancreatic adenocarcinoma xenografts

PV1 is an endothelial-specific protein with structural roles in the formation of diaphragms in endothelial cells of normal vessels. PV1 is also highly expressed on endothelial cells of many solid tumours. On the basis of in vitro data, PV1 is thought to actively participate in angiogenesis. To test whether or not PV1 has a function in tumour angiogenesis and in tumour growth in vivo, we have treated pancreatic tumour-bearing mice by single-dose intratumoural delivery of lentiviruses encoding for two different shRNAs targeting murine PV1. We find that PV1 down-regulation by shRNAs inhibits the growth of established tumours derived from two different human pancreatic adenocarcinoma cell lines (AsPC-1 and BxPC-3). The effect observed is because of down-regulation of PV1 in the tumour endothelial cells of host origin, PV1 being specifically expressed in tumour vascular endothelial cells and not in cancer or other stromal cells. There are no differences in vascular density of tumours treated or not with PV1 shRNA, and gain and loss of function of PV1 in endothelial cells does not modify either their proliferation or migration, suggesting that tumour angiogenesis is not impaired. Together, our data argue that down-regulation of PV1 in tumour endothelial cells results in the inhibition of tumour growth via a mechanism different from inhibiting angiogenesis.

AGR2 is a SMAD4-suppressible gene that modulates MUC1 levels and promotes the initiation and progression of pancreatic intraepithelial neoplasia

The mechanisms controlling expression of the putative oncogene AGR2 in pancreatic ductal adenocarcinoma (PDAC) are not well understood. We now show that AGR2 is a TGF-β-responsive gene in human pancreatic cancer cells, whose down-regulation is SMAD4-dependent. We also provide evidence supporting a role for AGR2 as an ER-chaperone for the cancer-associated mucin, MUC1. AGR2 is both sufficient and required for MUC1 expression in pancreatic cancer cells. Furthermore, AGR2 is co-expressed with MUC1 in mouse pancreatic intraepithelial neoplasia (mPanIN)-like lesions and in the cancer cells of four distinct genetically engineered mouse models of PDAC. We also show that Pdx1-Cre/LSL-Kras^G12D/Smad4^lox/lox mice heterozygous for Agr2 exhibit a delay in mPanIN initiation and progression to PDAC. It is proposed that loss of Smad4 may convert TGF-β from a tumor suppressor to a tumor promoter by causing the up-regulation of AGR2, which then leads to increased MUC1 expression, at which point both AGR2 and MUC1 facilitate mPanIN initiation and progression to PDAC.

Invasive mucinous cystic neoplasms of the pancreas

Mucinous cystic neoplasms (MCN) and intraductal papillary mucinous neoplasms (IPMN) of the pancreas both appear to have been included and intermixed in some early reports of pancreatic cystic neoplasms. Recognition of their distinguishing features evolved during the last decade of the twentieth century. One legacy of the early period is the statement that mucinous cystic neoplasms sometimes progress to invasive colloid carcinoma. It is now recognized that colloid carcinomas characteristically arise from IPMN. We set out to see if we could find MCN that invaded as colloid carcinomas and found no examples in MCN collected in two academic medical centers. We then sought to expand the number of MCN by evaluating series from additional centers. This yielded no examples of colloid carcinomas associated with 291 MCN, however one MCN exhibited a minor component with colloid (non-cystic mucinous) growth pattern within the fibrous wall of the neoplasm. The expression of CDX2, a marker of intestinal differentiation that is found in colloid carcinomas was examined by immunostaining in the original MCN series and in the MCN with the intratumoral colloid growth pattern. Focal expression of CDX2 was found in 22 of 43 MCN including the MCN that exhibited the intratumoral colloid growth pattern. Overall, the data suggest that MCN rarely, if ever, invade as colloid carcinoma but the expression of CDX2 by some MCN and the observation of intratumoral colloid growth pattern in one MCN seems to leave open the possibility that MCN might rarely invade as colloid carcinoma. The majority of malignant MCN invade with a tubular (ductal) pattern, and rarely the invasive component was anaplastic.

Intracellular activation of trypsinogen in transgenic mice induces acute but not chronic pancreatitis

BACKGROUND AND AIMS

Premature intra-acinar activation of trypsinogen is widely considered key for both the initiation of acute pancreatitis and the development of chronic pancreatitis. However, the biological consequences of intracellular trypsinogen activation have not been directly examined. To do so, a new mouse model was developed.

METHODS

Mice were engineered to conditionally express an endogenously activated trypsinogen within pancreatic acinar cells (PACE-tryp(on)). Hallmarks of pancreatitis were determined and findings were correlated to the level (zygosity) and extent (temporal and spatial) of conditional PACE-tryp(on) expression. Furthermore, the impact of acinar cell death in PACE-tryp(on) mice was assessed and compared with a model of selective diphtheria toxin (DT)-mediated induction of acinar apoptosis.

RESULTS

Initiation of acute pancreatitis was observed with high (homozygous), but not low (heterozygous) levels of PACE-tryp(on) expression. Subtotal (maximal-rapid induction) but not limited (gradual-repetitive induction) conditional PACE-tryp(on) expression was associated with systemic complications and mortality. Rapid caspase-3 activation and apoptosis with delayed necrosis was observed, and loss of acinar cells led to replacement with fatty tissue. Chronic inflammation or fibrosis did not develop. Selective depletion of pancreatic acinar cells by apoptosis using DT evoked similar consequences.

CONCLUSIONS

Intra-acinar activation of trypsinogen is sufficient to initiate acute pancreatitis. However, the primary response to intracellular trypsin activity is rapid induction of acinar cell death via apoptosis which facilitates resolution of the acute inflammation rather than causing chronic pancreatitis. This novel model provides a powerful tool to improve our understanding of basic mechanisms occurring during pancreatitis.

Deletion of Rb accelerates pancreatic carcinogenesis by oncogenic Kras and impairs senescence in premalignant lesions

BACKGROUND & AIMS

Rb1 encodes a cell-cycle regulator that is functionally disrupted in most human cancers. Pancreatic ductal adenocarcinomas (PDACs) have a high frequency of mutations in KRAS and INK4A/CDKN2A that might allow cells to bypass the regulatory actions of retinoblastoma (RB). To determine the role of loss of RB function in PDAC progression, we investigated the effects of Rb disruption during pancreatic malignant transformation initiated by oncogenic Kras.

METHODS

We generated mice with pancreas-specific disruption of Rb, in the absence or presence of oncogenic Kras, to examine the role of RB in pancreatic carcinogenesis.

RESULTS

In the presence of oncogenic Kras, loss of Rb from the pancreatic epithelium accelerated formation of pancreatic intraepithelial neoplasia (PanIN), increased the frequency of cystic neoplasms, and promoted rapid progression toward PDAC. Early stage cancers were characterized by acute pancreatic inflammation, associated with up-regulation of proinflammatory cytokines within the pancreas. Despite the presence of markers associated with oncogene-induced senescence, low-grade PanIN were highly proliferative and expressed high levels of p53. Pancreatic cancer cell lines derived from these mice expressed high levels of cytokines, and transcriptional activity of p53 was impaired.

CONCLUSIONS

Rb encodes a tumor suppressor that attenuates progression of oncogenic Kras-induced carcinogenesis in the pancreas by mediating the senescence response and promoting activity of the tumor suppressor p53.

MicroRNA-10b expression correlates with response to neoadjuvant therapy and survival in pancreatic ductal adenocarcinoma

INTRODUCTION

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy. Diagnosis and management of PDAC are hampered by the absence of sensitive and specific disease biomarkers. MicroRNAs (miRNA) are noncoding regulatory RNAs involved in initiation and progression of human cancers. In this study, we sought to determine whether miR-10b could serve as a biomarker for PDAC.

EXPERIMENTAL DESIGN

miRNA expression was characterized by fluorescence-based in situ hybridization using locked nucleic acid-modified DNA probes against miR-10b, miR-21, miR-155, miR-196a, and miR-210, followed by codetection of proteins by immunohistochemistry on the same tissue sections. miRNA expression in surgically resected PDAC tissues and in endoscopic ultrasonography (EUS)-guided fine-needle aspirate (EUS-FNA) samples was analyzed in cytokeratin 19 (CK19)-positive epithelial cells using optical intensity analysis.

RESULTS

In 10 resected PDAC samples, miR-10b was the most frequently and consistently overexpressed miRNA among characterized miRNAs, exhibiting a four-fold increase in the cancer cells (P = 0.012). Given this preferential overexpression of miR-10b, we sought to determine whether miR-10b expression was clinically relevant. Accordingly, miR-10b expression was examined in 106 EUS-FNA samples obtained from pancreatic lesions. miR-10b expression was increased in cancer cells compared with CK19-positive epithelial cells in benign lesions (P = 0.0001). In patients with PDACs, lower levels of miR-10b were associated with improved response to multimodality neoadjuvant therapy, likelihood of surgical resection, delayed time to metastasis, and increased survival.

CONCLUSION

miR-10b is a novel diagnostic biomarker for PDACs when assessing pancreatic lesions. Expression of miR-10b is predictive of response to neoadjuvant therapy and outcome in this disease.

Growing colorectal tumors: minimizing microbial and stromal competition and assessing in vitro selection pressures

Development of primary colorectal cancer cell lines ishampered by contamination from regional microbes, overgrowthof stromal cells, and purported genetic drift from selectionpressures in vitro. We initiated 32 primaryadenocarcinomas, 3 recurrences and 6 distant metastases incell culture. Twelve cell lines from eleven tumors weregenerated (26.8%) overall. Nine of 32 primary tumorsyielded 10 cell lines, 5 were lost to contamination, 13 wereoverwhelmed by stromal cells, and 5 demonstrated no growth.Addition of isobutyl methyl xanthine (IBMX) to culturelimited fibroblastoid growth. There was no associationbetween tumor location (p = 0.535, mid-P), degree ofdifferentiation (p = 0.850, mid-P) or clinicopathologic stage(p = 0.400, mid-P), and the ability of cells to becomeestablished in culture. The majority of cell lines hadsimilar nuclear DNA content and expression of cell-surfaceantigens compared with their parent tumors. Microbialcontamination and stromal cell overgrowth present thegreatest obstacle to capturing a representative bank ofcolon tumors in vitro.

Ras activity levels control the development of pancreatic diseases

BACKGROUND & AIMS

Differentiated pancreatic acinar cells expressing endogenous levels of mutant K-Ras do not spontaneously develop pancreatic ductal adenocarcinoma (PDAC). However, we hypothesized that acinar cells would develop PDAC in the presence of Ras activity levels mimicking those of human tumor cells.

METHODS

We measured Ras activity in PDAC cells from mice and humans using a Raf pull-down assay. We compared the effects of acinar cell expression of mutant K-Ras at endogenous and elevated levels on Ras activity and on the development of PDAC.

RESULTS

Ras activity was greatly elevated in PDAC cells compared with nontransformed cells expressing endogenous levels of mutant K-Ras. Expression of endogenous levels of mutant K-Ras in differentiated acinar cells resulted in moderately elevated Ras activity and in sparse murine pancreatic intraepithelial neoplasias (mPanINs) that did not spontaneously advance to PDAC unless the tumor suppressor p53 was simultaneously deleted. In contrast, expression of mutant K-Ras at higher levels generated Ras activity equal to that in PDAC. High Ras activity mimicking levels in PDAC led to acinar cell senescence and generated inflammation and fibrosis resembling the histologic features of chronic pancreatitis. With higher Ras activity in acinar cells, abundant mPanINs formed and spontaneously progressed to both cystic papillary carcinoma and metastatic PDAC.

CONCLUSIONS

There is an important relationship between Ras activity levels and the progression of PDAC. Sufficient Ras activity in pancreatic acinar induces several important pancreatic disease manifestations not previously reported and supports a potential direct linkage between chronic pancreatitis, cystic papillary carcinoma, and PDAC.

Pancreatic cancer and precursor pancreatic intraepithelial neoplasia lesions are devoid of primary cilia

Primary cilia have been proposed to participate in the modulation of growth factor signaling pathways. In this study, we determined that ciliogenesis is suppressed in both pancreatic cancer cells and pancreatic intraepithelial neoplasia (PanIN) lesions in human pancreatic ductal adenocarcinoma (PDAC). Primary cilia were absent in these cells even when not actively proliferating. Cilia were also absent from mouse PanIN cells in three different mouse models of PDAC driven by an endogenous oncogenic Kras allele. Inhibition of Kras effector pathways restored ciliogenesis in a mouse pancreatic cancer cell line, raising the possibility that ciliogenesis may be actively repressed by oncogenic Kras. By contrast, normal duct, islet, and centroacinar cells retained primary cilia in both human and mouse pancreata. Thus, arrested ciliogenesis is a cardinal feature of PDAC and its precursor PanIN lesions, does not require ongoing proliferation, and could potentially be targeted pharmacologically.

The Nestin progenitor lineage is the compartment of origin for pancreatic intraepithelial neoplasia

To determine the cell compartment in which initial oncogenic mutations occur in pancreatic ductal adenocarcinoma (PDAC), we generated a mouse model in which endogenous expression of mutated Kras (Kras(G12D)) was initially directed to a population of pancreatic exocrine progenitors characterized by the expression of Nestin. Targeting of oncogenic Kras to such a restricted cell compartment was sufficient for the formation of pancreatic intraepithelial neoplasias (PanINs), putative precursors to PDAC. PanINs appeared with the same grade and frequency as observed when Kras(G12D) was targeted to the whole pancreas by a Pdx1-driven Cre recombinase strategy. Thus, the Nestin cell lineage is highly responsive to Kras oncogenic activation and may represent the elusive progenitor population in which PDAC arises.

Solid serous adenoma of the pancreas: a rare variant within the family of pancreatic serous cystic neoplasms

We report the third case of a solid serous adenoma of the pancreas, a rare variant of tumor within the family of pancreatic serous cystic neoplasms. This asymptomatic tumor presented in a 66-year-old man during imaging for another problem. Computed tomography of the abdomen demonstrated a 3.5-cm hypervascular mass in the head of the pancreas. A pylorus preserving pancreaticoduodenectomy was performed. Histological examination demonstrated a neoplasm identical to a serous cystadenoma-glycogen-rich cuboidal or polygonal cells with finely granulated eosinophilic or clear cytoplasm. More often, the neoplasm contained solid areas and tubules but no microcysts. Periodic acid Schiff's-glycogen staining was positive in some cells, turning negative after diastase was applied. Immunostaining was positive for CK7, CK8, neuron specific enolase, and MUC6. The microscopic findings of a solid neoplasm of cuboidal cells rich in glycogen and the immunostaining listed associate this tumor with the previously 2 reported cases of solid serous adenoma. All 3 reported cases thus far have proven to be benign lesions by pathological examination. Because clinical follow-up is reported only in the present case, caution should be exercised in declaring the solid serous adenoma of the pancreas as a benign lesion.

Pathology of genetically engineered mouse models of pancreatic exocrine cancer: consensus report and recommendations

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.

'If it isn't published, it isn't research.' An interview with Professor Daniel S. Longnecker, by Martin E. Fernandez-Zapico

Daniel Longnecker is a worldwide-recognized pancreatologist for his contribution to the understanding of the pathogenesis of pancreatic diseases. He was a pioneer in the development of animal models for pancreatic disorders, in particular pancreatic cancer. In addition, he led the way in the characterization and classification of the lesions involved in pancreatic neoplasias. In this interview, Professor Longnecker comments on his experience in pancreatic research and provides advice to new investigators in this field.

Histopathological diagnosis of pancreatic intraepithelial neoplasia and intraductal papillary-mucinous neoplasms: interobserver agreement

OBJECTIVES

The goal of this study was to evaluate the consistency of distinction between pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary-mucinous neoplasms (IPMN) and the hypothesis that guidelines for their distinction might be inadequate.

METHODS

A group of 93 pancreas specimens from surgical resections or autopsies that contained lesions consistent with histopathological diagnoses of PanIN-1A, PanIN-1B, PanIN-2, or IPMN (adenoma or borderline) was collected. The classification of these neoplasms by 6 pathologists, 2 from Europe, 2 from Japan, and 2 from the United States, was compared. The pathologists initially used guidelines current in their practice and then reviewed 47 of the 93 specimens a second time using new consensus definitions and guidelines for PanIN and IPMN that were developed in 2003.

RESULTS

The initial comparison showed frequent disagreement regarding both category and grade of the lesions. Agreement was greater for category than grade. In the second review, agreement among the 6 reviewers improved, remaining higher for category, although disagreements persisted for both category and grade.

CONCLUSIONS

We conclude that the new definitions of PanIN and IPMN improve the consistency in classifying these lesions, but additional work is needed to further improve the reproducibility of their classification.

Classification of types of intraductal papillary-mucinous neoplasm of the pancreas: a consensus study

Now that more than two decades have passed since the first reports of intraductal papillary-mucinous neoplasms (IPMNs), it has become clear that IPMN consists of a spectrum of neoplasms with both morphological and immunohistochemical variations. At a meeting of international experts on pancreatic precursor lesions held in 2003, it was agreed that a consensus classification of IPMN subtypes should be established to enable a more detailed analysis of the clinicopathological significance of the variations. Based on our experience and on information from the literature, we selected representative histological examples of IPMNs and defined a consensus nomenclature and criteria for classifying variants as distinctive IPMN subtypes including gastric type, intestinal type, pancreatobiliary type, and oncocytic type. These definitions can be used for further analyses of the clinicopathological significance of the variations of IPMN.

An experimental model of autoimmune pancreatitis in the rat

Autoimmune pancreatitis (AIP), a recently defined disease of unknown etiology, is characterized by inflammatory infiltrates in the pancreas with conspicuous involvement of the ducts. The disease clinically manifests in humans as epigastric pain, weight loss, and jaundice. This report describes the development of a novel animal model of this disease in the rat, which we have termed experimental autoimmune pancreatitis. Adoptive transfer of amylase-specific CD4(+) T cells was able to confer pancreatitis to naive syngeneic recipient animals. No treatments before the adoptive transfer of T cells were necessary for disease to ensue, and the severity of disease was proportional to the number of T cells administered. The pancreatic lesions of rats with experimental autoimmune pancreatitis were characterized histologically as overwhelmingly lymphocytic with occasional plasma cells, neutrophils, and mast cells. Acinar tissue destruction and ductular inflammation were common features, with less frequent involvement of larger ducts. Immunohistochemical analysis revealed the presence of CD4(+) T cells in large numbers as well as CD8(+) T cells, macrophages, and dendritic cells. Expression of MHC I and MHC II also increased at the site of the lesion. Clinically, the disease manifested as either failure to gain weight at a rate concomitant with control animals or as outright weight loss. Thus, administration of activated CD4(+) T cells specific for the pancreatic enzyme amylase can induce pancreatitis in the rat in a manner that is reminiscent of human AIP.

An illustrated consensus on the classification of pancreatic intraepithelial neoplasia and intraductal papillary mucinous neoplasms

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.

Preinvasive pancreatic neoplasia of ductal phenotype induced by acinar cell targeting of mutant Kras in transgenic mice

Activating mutation of the Kras oncogene is the most frequent and perhaps the earliest genetic alteration associated with pancreatic cancer. To examine the link between mutant Kras and exocrine pancreatic cancer, we generated transgenic mice carrying an elastase-mutant Kras transgene, which targets expression to pancreatic acinar cells. Most elastase-Kras founder mice displayed perinatal pancreatic acinar cell hyperplasia and dysplasia. However, adult mice in two surviving lineages displayed preinvasive pancreatic neoplastic lesions with ductal morphology, thereby providing a unique mouse model in which lesion histotype and initiating genetic alteration overlap with the human disease. Our findings suggest that Kras mutation is associated with development of early stage duct-like lesions in pancreas, but that additional alterations must accompany progression to malignancy.

The dichotomy in the preinvasive neoplasia to invasive carcinoma sequence in the pancreas: differential expression of MUC1 and MUC2 supports the existence of two separate pathways of carcinogenesis

Emerging evidence suggests a dichotomy in the dysplasia-CIS-invasive carcinoma sequence in the pancreas. Pancreatic intraepithelial neoplasms (PanINs; small, incidental duct lesions) progress to invasive ductal adenocarcinomas (5-y survival of < 15%), whereas intraductal papillary mucinous neoplasms (large, intraductal tumors with ductal dilatation) are often associated with colloid carcinoma (5-y survival of > 55%). We explored the relationship of these lesions by examining the expression of MUC1 and MUC2, glycoproteins reportedly reflecting "aggressive" and "indolent" phenotypes in pancreas cancer, respectively. Immunohistochemical labeling with MUC1 (clone Ma695) and MUC2 (clone Ccp58) antibodies was performed on PanINs (n = 43), intraductal papillary mucinous neoplasms (n = 74), ductal adenocarcinomas (n = 136), and colloid carcinomas (n = 15). Fifty-four percent of the intraductal papillary mucinous neoplasms expressed MUC2, whereas none of the PanINs did. In contrast, PanINs, especially higher grade lesions, were often positive for MUC1 (61% of PanIN 3), whereas the expression of this glycoprotein was infrequent in intraductal papillary mucinous neoplasms (20%). This dichotomy was further accentuated in the invasive carcinomas with which these two preinvasive pathways are respectively associated: all colloid carcinomas were MUC2+ (100%) and MUC1- (0%), whereas the labeling pattern was the reverse for ductal adenocarcinomas: 63% were MUC1+ and only 1% were MUC2+. These results support a dichotomy in the dysplasia-CIS sequence in the pancreas. Because these two pathways often lead to different types of invasive carcinomas, this is an invaluable model for the study of carcinogenesis. The findings here also support the previous impression that MUC2 (the mucin associated with gel formation) is a marker of the "indolent" pathway (intraductal papillary mucinous neoplasm and colloid carcinoma), whereas MUC1 (the glycoprotein known to have an inhibitory role in cell-cell and cell-stroma interactions as well as in immunoresistance of tumor cells) is a marker of the "aggressive" pathway (PanIN to ductal adenocarcinoma).

Deoxyribonuclease IIalpha is required during the phagocytic phase of apoptosis and its loss causes perinatal lethality

Deoxyribonuclease IIalpha (DNase IIalpha) is one of many endonucleases implicated in DNA digestion during apoptosis. We produced mice with targeted disruption of DNase IIalpha and defined its role in apoptosis. Mice deleted for DNase IIalpha die at birth with many tissues exhibiting large DNA-containing bodies that result from engulfed but undigested cell corpses. These DNA-containing bodies are pronounced in the liver where fetal definitive erythropoiesis occurs and extruded nuclei are degraded. They are found between the digits, where apoptosis occurs, and in many other regions of the embryo. Defects in the diaphragm appear to cause death of the mice due to asphyxiation. The DNA in these bodies contains 3'-hydroxyl ends and therefore stain positive in the TUNEL assay. In addition, numerous unengulfed TUNEL-positive cells are observed throughout the embryo. Apoptotic cells are normally cleared rapidly from a tissue; hence the persistence of the DNA-containing bodies and TUNEL-positive cells identifies sites where apoptosis occurs during development. These results demonstrate that DNase IIalpha is not required for the generation of the characteristic DNA fragmentation that occurs during apoptosis but is required for degrading DNA of dying cells and this function is necessary for proper fetal development.

Abnormal methyl metabolism in pancreatic toxicity and diabetes

Several experimental studies suggest that disturbed methylation can influence cellular differentiation in the pancreas and contribute to toxic injury in ways that enhance the pathogenesis of pancreatitis and carcinogenesis. In vitro development of fetal rat pancreas requires a basal level of methionine, but full differentiation requires a higher methionine level. Involvement of methylation in normal differentiation is supported by reports of development of hepatocyte-like cells in the pancreas of rats fed a choline-deficient diet. The administration of ethionine by feeding to mice in a choline-sufficient diet caused a lower incidence of acute hemorrhagic pancreatitis than in mice given a choline-deficient diet. Feeding or injections of ethionine in choline-sufficient diets induces low grade pancreatitis and pancreatic atrophy in rats. In the N-nitrosobis(2-oxopropyl)amine-induced model of ductal adenocarcinoma in hamsters, the latent period for induction of carcinomas has been dramatically reduced by the intermittent feeding of a choline-deficient diet combined with ethionine treatment. A recent epidemiologic study in smokers indicates that the risk of pancreatic carcinoma is inverse to serum levels of folate. These studies suggest that compromised methyl metabolism might be associated with pancreatic cancer risk in humans. Finally, it has recently been demonstrated that serum homocysteine and erythrocyte S-adenosylhomocysteine levels are elevated, and erythrocyte S-adenosylmethionine content is reduced in patients with diabetes mellitus and renal failure, likely reflecting disturbed methylation pathways. The latter may contribute to the pathogenesis of complicating lesions in diabetes. These studies suggest that disturbed methyl metabolism may contribute to the pathogenesis of several pancreatic diseases.

Effect of hypergastrinemia on pancreatic carcinogenesis

BACKGROUND

Previous studies in our laboratory demonstrated that pancreatic carcinomas in rodents express receptors for the peptide hormone gastrin that are not present in normal adult pancreas. In view of an abundant literature suggesting that gastrin may promote growth of various gastrointestinal tissues and tumors, the effect of hypergastrinemia on the process of pancreatic carcinogenesis was evaluated.

METHODS

Rats received subcutaneous injections of the pancreatic carcinogen azaserine at 19 and 26 days of age. Starting at 12 months of age, animals were randomized to treatment with the proton pump inhibitor lansoprazole or vehicle by gavage for 6 months. At autopsy, pancreatic wet weight normalized to body weight was recorded, as well as the number of benign and malignant pancreatic lesions.

RESULTS

Serum gastrin levels were determined by radioimmunoassay and showed a greater than two-fold increase in lansoprazole-treated animals. Pancreatic wet weight in hypergastrinemic rats was increased compared to controls (p <0.05). Premalignant lesions such as acidophilic atypical acinar cell foci, adenomas, heterogeneous phenotypic populations of nodules within nodules, and carcinoma-in-situ were not increased in the hypergastrinemic group. Likewise, there was no difference in the incidence of invasive carcinoma in hypergastrinemic animals (10%) compared to controls (5.7%).

CONCLUSION

Hypergastrinemia stimulated an increase in pancreatic weight, but did not stimulate development of premalignant lesions or progression to cancer in the azaserine model of rat pancreatic acinar cell carcinoma.

Mixed acinar-endocrine carcinoma arising in the ampulla of Vater

We present a case of mixed acinar-endocrine carcinoma arising in the periampullary region of the duodenum. The patient was a 78-year-old male with a periampullary mass diagnosed during upper endoscopy. On gross dissection, the mass was 2.3 cm in diameter, noncystic, and confined to the duodenal submucosa. Microscopically, the tumor formed nests that were positive for amylase, trypsin (weakly), and synaptophysin (diffusely). Ultrastructurally, the tumor had 2 populations of granules with mean diameters of 175 nm and 540 nm, consistent with endocrine and zymogen granules, respectively. These studies were consistent with a mixed acinar-endocrine carcinoma that arose in the duodenum. A review of the literature revealed 1 report of an acinar cell carcinoma arising in jejunal pancreatic heterotopia. The present article is the first reported case of an acinar cell carcinoma arising in the periampullary region of the duodenum, possibly in a focus of pancreatic heterotopia.

Pancreatic intraepithelial neoplasia: a new nomenclature and classification system for pancreatic duct lesions

Proliferative epithelial lesions in the smaller caliber pancreatic ducts and ductules have been the subject of numerous morphologic, clinical, and genetic studies; however, a standard nomenclature and diagnostic criteria for classifying these lesion have not been established. To evaluate the uniformity of existing systems for grading duct lesions in the pancreas, 35 microscopic slides with 35 representative duct lesions were sent to eight expert pathologists from the United States, Canada, and Europe. Kappa values for interobserver agreement could not be calculated initially because more than 70 different diagnostic terms were used by the eight pathologists. In several cases, the diagnoses rendered for a single duct lesion ranged from "hyperplasia," to "metaplasia," to "dysplasia," to "carcinoma in situ." This review therefore demonstrated the need for a standard nomenclature and classification system. Subsequently, during a working group meeting, the pathologists agreed to adopt a single standard system. The terminology pancreatic intraepithelial neoplasia (or PanIN) was selected, and diagnostic criteria for each grade of PanIN were established (http://pathology.jhu.edu/pancreas_panin). This new system was then evaluated by having the eight pathologists rereview the original 35 cases. Only seven different diagnoses were rendered, and kappa values of 0.43, 0.14, and 0.42 were obtained for PanINs 1, 2, and 3 respectively. Cases assigned other diagnoses (e.g., squamous metaplasia) collectively had a kappa value of 0.41. These results show both the potential of the classification system, and also the difficulty of classifying these lesions even with a consistent nomenclature. However, even when there is lack of consensus, having a restricted set of descriptions and terms allows a better understanding of the reasons for disagreement. It is suggested that we adopt and apply this system uniformly, with continued study of its reliability and use, and possibly further refinement. The acceptance of a standard classification system will facilitate the study of pancreatic duct lesions, and will lead ultimately to a better understanding of their biologic importance.

Racial differences in pancreatic cancer: comparison of survival and histologic types of pancreatic carcinoma in Asians, blacks, and whites in the United States

SEER data for histologically confirmed carcinomas of the pancreas for 1973-1995 from Hawaii, San Francisco, and Seattle (n = 10,621) were analyzed to compare the survival and types of carcinomas in various racial groups. These geographic sites were selected because each included a sizable number of Asian patients. The median survival after diagnosis in unadjusted data was longer in Asian patients than in whites. After adjustment for age at diagnosis and year of diagnosis, only the survival advantage of Asian women over whites and blacks persisted as a statistically significant difference. Racial differences were no longer statistically significant when further adjustments were made for stage, grade, and morphology. The proportion of papillary carcinomas or mucinous cystadenocarcinomas was higher in Asians than in whites and blacks (p = 0.02), and patients with these neoplasms had a longer median survival than did patients with ductal adenocarcinoma (12 vs. 3.3 months). The fraction of Asian patients with lower stages and grades of carcinomas also was higher than among white and black patients. Longer survival of Asian compared with white and black patients with pancreatic carcinoma is at least partly explained by their higher proportion of less aggressive carcinomas at the time of diagnosis.

Simultaneous mucinous cystadenoma of ovary and mucinous cystadenocarcinoma of pancreas

Mucinous cystic tumors were discovered synchronously in the tail of the pancreas and in the right ovary of an adult female. Both tumors were amenable to surgical resection. The pancreatic tumor was a noninvasive mucinous cystadenocarcinoma and the ovarian tumor was a mucinous cystadenoma. We feel these tumors represent two primaries, an uncommon occurrence, and not a single primary tumor with metastasis.

Vascular structure and microcirculation of experimental pancreatic carcinoma in rats

OBJECTIVE

To study angiogenesis and microcirculation in experimental pancreatic carcinoma.

DESIGN

Open experimental study.

SETTING

2 University hospitals, Germany and USA.

ANIMALS

16 male Lewis rats.

INTERVENTIONS

Induction of a duct-like pancreatic cancer in the pancreas and peritoneum by interposition of fragments of tumour between 2 inert transparent polymethylmethacrylate plates.

MAIN OUTCOME MEASURES

Microcirculation in the tumour and interaction between leucocytes, tumour, and endothelium investigated by intravital microscopy.

RESULTS

The density of vessels in the carcinoma was significantly less than in normal pancreatic tissue (p = 0.0004). The vasculature of the tumour was characterised by a lack of differentiation in architecture of vessels, formation of sinusoidal and lacunar vessels and sudden changes in diameter of vessels. Red blood cell velocity differed among tumour vessels, but mean values were similar to those of normal exocrine pancreas. The mixed lymphocyte culture test indicated that the cell line DSL6A was immunogenic. However, high-affinity leucocyte-endothelium-interaction was significantly reduced in the tumour's microcirculation after both orthotopic and heterotopic implantation (p = 0.002). Rates of apoptosis were suppressed in heterotopic tumours compared with orthotopic ones. Tumour growth was faster in heterotopic tumours.

CONCLUSIONS

Experimental duct-like pancreatic carcinoma can be differentiated from normal pancreas by: chaotic arrangement of vessels with loss of differentiation of architecture and heterogeneous distribution; the formation of sinusoidal or lacunar vessels; lower vascular density with similar erythrocyte velocity; increase in mean diameter of vessels; reduced leucocyte-endothelium interaction despite confirmed immunogeneity independent of wall shear rates. The site of implantation influences apoptosis and growth rates.

Role of the basic helix-loop-helix transcription factor p48 in the differentiation phenotype of exocrine pancreas cancer cells

The majority of human pancreatic adenocarcinomas display a ductal phenotype; experimental studies indicate that tumors with this phenotype can arise from both acinar and ductal cells. In normal pancreas acinar cells, the pancreas transcription factor 1 transcriptional complex is required for gene expression. Pancreas transcription factor 1 is a heterooligomer of pancreas-specific (p48) and ubiquitous (p75/E2A and p64/HEB) basic helix-loop-helix proteins. We have examined the role of p48 in the phenotype of azaserine-induced rat DSL6 tumors and cancers of the human exocrine pancreas. Serially transplanted acinar DSL6 tumors express p48 whereas DSL6-derived cell lines, and the tumors induced by them, display a ductal phenotype and lack p48. In human pancreas cancer cell lines and tissues, p48 is present in acinar tumors but not in ductal tumors. Transfection of ductal pancreas cancers with p48 cDNA did not activate the expression of amylase nor a reporter gene under the control of the rat elastase promoter. In some cell lines, p48 was detected in the nucleus whereas in others it was cytoplasmic, as in one human acinar tumor. Together with prior work, our findings indicate that p48 is associated with the acinar phenotype of exocrine pancreas cancers and it is necessary, but not sufficient, for the expression of the acinar phenotype.

Pancreatic tumors with cystic dilatation of the ducts: intraductal papillary mucinous neoplasms and intraductal oncocytic papillary neoplasms

Intraductal papillary mucinous neoplasms (IPMNs) and intraductal oncocytic papillary neoplasms (IOPNs) are the 2 types of intraductal neoplasms of the pancreas that may appear cystic because of dilatation of the ducts. Both are characterized by intraductal proliferation of mucinous cells usually arranged in papillary patterns. This proliferation is often associated with intraluminal mucin accumulation, which produces cystic dilatation of the ducts, mimicking mucinous cystic neoplasms. Endoscopic and radiologic studies and careful macroscopic examination are crucial for the correct diagnosis of IPMNs and IOPNs by showing the origin within the native ducts. Microscopically, these tumors display a spectrum of cytoarchitectural atypia that ranges from adenoma to borderline and to carcinoma-in-situ. Although they are defined as "intraductal tumors," IPMNs and IOPNs are associated with invasive carcinoma in about a third of the cases. It, therefore, appears that, like mucinous cystic neoplasms or pancreatic intraepithelial neoplasia involving the smaller ducts associated with ordinary ductal adenocarcinomas, these tumors are precursors of invasive carcinoma. Invasive carcinomas associated with IPMNs are of either tubular or colloid (mucinous noncystic) types, whereas those associated with IOPNs may be oncocytic. Even in the presence of invasive carcinoma, these tumors may follow a more protracted clinical course than ordinary ductal adenocarcinoma. On the other hand, rare examples of IPMNs after an aggressive clinical course despite the lack of any identifiable invasive carcinoma are on record. Therefore, IPMNs and IOPNs should be examined carefully and sampled extensively, first, to confirm that the main pathology is an intraductal process and, more importantly, to rule out the presence of an invasive carcinoma.

Molecular pathology of invasive carcinoma

Abnormalities of several oncogenes and tumor suppressor genes have been identified in carcinomas of the pancreas during the last decade, and multiple genetic changes have been demonstrated in individual carcinomas. The variety of genetic changes suggests that multiple etiologic factors contribute to carcinogenesis in the pancreas. Several of these changes are characteristically found in specific types of tumors, suggesting that different causes and molecular mechanisms are involved. One example is the loss of heterozygosity at the von Hippel-Lindau (VHL) gene locus in both wild type and hereditary serous cystadenomas, and another is the virtual absence of K-ras mutation and p53 abnormalities in acinar cell carcinomas, whereas both are frequently found in ductal adenocarcinomas. Multiple lines of evidence place K-ras mutation very early and loss of p53 and p16 as late events during ductal cell carcinogenesis. The timing and order of other genetic changes such as loss of the DPC4 tumor suppressor function is less certain.

Observations on the etiology and pathogenesis of intraductal papillary-mucinous neoplasms of the pancreas

During the last two decades, intraductal papillary-mucinous neoplasms have been recognised as a group that should be distinguished from ductal adenocarcinomas. The literature for these tumors is confusing with the use of many different terms such as mucinous duct ectasia and, sometimes, there is a failure to distinguish them from mucinous cystic tumors. The recognition and apparently increasing incidence of these neoplasms is perhaps entirely attributable to improved diagnostic and imaging methods such as endoscopic retrograde pancreatography and computerized tomography. Experimental, molecular, and epidemiologic data suggest that the etiology of IPMN overlaps that of solid ductal adenocarcinomas.

Mechanistic analysis and chemoprevention of pancreatic carcinogenesis

Thirteen presentations given at a workshop held in November 1997, under the sponsorship of The Princess Takamatsu Cancer Research Fund in Nara, Japan, are summarized. Topics include studies of initiation, promotion, and chemoprevention in animal models of pancreatic carcinogenesis, molecular and histopathologic studies of human carcinomas, and epidemiologic studies. A recurring focus was to explore ways that knowledge of molecular mechanisms of carcinogenesis and molecular abnormalities in carcinomas can guide approaches for prevention and treatment of pancreatic cancer.

K-ras mutation in focal proliferative lesions of human pancreas

The K-ras gene is mutated in > or =75% of human pancreatic adenocarcinomas and in a number of hyperplastic ductal lesions from noncarcinoma patients. In this study, the incidence of K-ras mutation was determined in a spectrum of focal proliferative pancreatic lesions to evaluate their preneoplastic significance. PCR-based mutation-enriched RFLP analysis was used to identify mutations in codon 12. Immunostaining for Ki67 and p53 was also performed. Forty-seven % of intraductal nonpapillary hyperplasias (8 of 17) contained codon 12 mutations, as did 55% of adenomatoid hyperplasias (6 of 11). This rate increased to 61% in papillary hyperplasias (27 of 44) and to 78% when there was severe dysplasia (7 of 9). The fraction of cells staining for the Ki67 proliferation marker showed a general correlation with the rate of K-ras mutation. Nuclear staining for p53 protein was seen only in two ductal lesions with severe dysplasia. No mutations were found in normal acinar tissue (n = 38), squamous metaplasia (n = 13), ductal complexes (n = 8), or focal acinar cell dysplasia (n = 5). There seemed to be a general correlation of proliferative potential with the presence of K-ras mutation in ductal lesions. However, because of the high prevalence of lesions with K-ras mutations, we conclude that this mutation alone cannot be taken as proof of significant risk for progression to carcinoma. Efforts to use the presence of K-ras mutations in DNA harvested from pancreatic juice or duodenal aspirates as an approach for diagnosis of occult pancreatic carcinoma seem vulnerable to a high false-positive rate.

Azaserine-induced rat pancreas tumor model with transplantable cultured cells

The purpose of this study was to describe the inoculation technique and patterns of growth as well as to characterize typical histological features of Lewis rat subcutaneous and intrapancreatic tumors, induced by inoculation of cultured pancreatic cancer cells (DSL-6A/C1). Subcutaneous inoculation of cultured cells produced a solid tumor that was a locally invasive, well- to moderately differentiated ductal adenocarcinoma. Tumor take was 100% in animals 5 weeks of age; tumor growth was consistent and predictable and a tumor volume of approximately 1 cm3 was reached in 8 weeks. After intrapancreatic transplantation the tumors showed the same histological features as subcutaneous tumors. During inoculation carcinoma cells easily spread around the injected area, and after 2 weeks both pancreatic tumors and superficially infiltrating carcinomas were found in the liver and spleen and around the peritoneum. Tumor take was 60% and tumor growth was somewhat indefinite and unpredictable in the pancreas. However, by reducing the injected carcinoma cell volume and solving the technical problems, 100% tumor take was achieved. The tumor volume reached 2 mm3 during 2 weeks and larger tumors showed a tendency for invasion. According to our results, subcutaneous as well as intrapancreatic tumor induction with cultured cells offers a model for pancreatic cancer studies.

Evaluation of p53 mutation in pancreatic acinar cell carcinomas of humans and transgenic mice

Mutation of the p53 tumor suppressor gene is found in a large number of exocrine pancreatic tumors. The majority of these tumors is of the ductal cell phenotype. We examined 12 human acinar cell carcinomas and 42 transgenic mouse carcinomas (including 36 acinar cell tumors, four islet cell tumors, and two liver metastases of primary acinar cell tumors) for evidence of p53 mutation. Immunohistochemistry was used to identify p53 protein in tumor sections. To evaluate p53 exons 5-8, heteroduplex analysis was used on formalin-fixed, paraffin-embedded human tumor DNA, and single-strand conformation polymorphism analysis was used on frozen mouse tumor DNA. No molecular evidence of p53 mutation was found in any of the tumor DNAs and immunohistochemical data were regarded as negative. This study provides evidence that acinar cell carcinogenesis in both humans and transgenic mice is independent of p53 mutation.

Mechanisms for the pancreatic oncogenic effects of the peroxisome proliferator Wyeth-14,643

Several peroxisome proliferators have been shown to produce pancreatic acinar cell hyperplasia/adenocarcinomas in 2-year bioassays with rats: ammonium perfluorooctanoate (C8), clofibrate, methylclofenapate, HCFC-123, and Wyeth-14,643 (WY). We have used in vitro (C8, WY) and in vivo (WY) approaches to examine several possible mechanisms of pancreatic tumorigenesis by peroxisome proliferating compounds. These mechanisms include cholecystokinin receptor agonism (CCK(A)), trypsin inhibition, alterations in gut fat content, cholestasis, and altered bile flow/composition. All of these mechanisms enhance pancreatic growth either by binding to the CCK(A) receptor or by increasing plasma CCK levels. In vitro experiments using a receptor competition binding assay demonstrated that WY and C8 do not bind directly to the CCK(A) receptor. In a continuous spectrophotometric assay, WY and C8 also failed to inhibit trypsin, a common mechanism for increasing plasma CCK levels. These in vitro results suggested that WY was not acting via the two most common mechanisms for modulation of pancreas growth. Two types of in vivo experiments were conducted. The subchronic study (2-month duration) was designed primarily to detect early changes in pancreatic growth such as those mediated by compounds that inhibit trypsin or act as CCK(A) receptor agonists. The chronic study (6 months) was designed primarily to evaluate whether the pancreatic lesions were secondary to hepatic changes such as cholestasis and/or altered bile flow/composition. In the in vivo experiments, male Crl:CDBR rats were fed diets containing 0 or 100 ppm WY. In the subchronic study WY-treated rats had a twofold increase in mean relative liver weights, an eightfold increase in hepatic peroxisomal proliferation, and a fourfold increase in hepatocyte cell proliferation after 1 week which remained elevated throughout the 2 months of treatment. In contrast, no pancreatic weight effects, increases in plasma CCK, or acinar cell proliferation was seen through 2 months in the WY group when compared to the control group. Fecal fat concentrations were also measured at 2 months and demonstrated no difference between control and WY-treated animals. The absence of any early pancreas changes in the subchronic study is consistent with the in vitro data which demonstrated that WY is not a CCK(A) agonist or a trypsin inhibitor. The chronic study demonstrated increases in pancreatic weights at 3 months (6% above control) and 6 months (17% above control), as well as increased CCK plasma levels in the WY-treated group. Liver effects in the chronic study paralleled those of the subchronic time points. Clinical pathology endpoints including increased serum concentrations of bile acids, alkaline phosphatase, and bilirubin were indicative of cholestasis in the chronic WY-treated group. The cholestasis may be responsible for the downward trend in total bile acid output, both of which may contribute to the modest increases in plasma CCK levels. These results indicate that chronic exposure to WY causes liver alterations such as cholestasis, which may increase plasma concentrations of CCK. Hence, WY may induce pancreatic acinar cell adenomas/adenocarcinomas via a mild but sustained increase in CCK levels secondary to hepatic cholestasis.

Small intraductal papillary-mucinous adenomas of the pancreas

Intraductal papillary-mucinous tumors in the pancreas have recently been described as a distinct entity, but the classification of these neoplasms remains under debate. Of issue is the biologic potential of these lesions and the predictability of clinical behavior on the basis of histologic appearance. We report two cases with intraductal papillary tumors formed by highly differentiated mucin-containing columnar epithelium found incidentally at autopsy. Both were classified as adenomas on the basis of histologic features. Neither patient experienced symptoms from their lesion during life and both died of other causes. Both lesions were studied by the polymerase chain reaction and were found to harbor codon 12 mutations in the c-K-ras gene. The concept that these neoplasms represent an early stage in an adenoma-carcinoma sequence is discussed.

The case for parallel classification of biliary tract and pancreatic neoplasms

Most primary epithelial neoplasms found in the intrahepatic and extrahepatic biliary tracts and the pancreas have similar histologic appearances. The degree of similarity of tumor types is greater than is commonly appreciated and extends to rare neoplasms. It has been suggested that parallel classifications could be used for tumors arising in these sites. However, significant differences in terms used to denote histologically identical neoplasms are found in the current World Health Organization (WHO) classification of biliary tract tumors and the new WHO classification of exocrine pancreatic neoplasms. Mutations of oncogenes and abnormalities of tumor suppressor genes found in ductal adenocarcinomas from the two sites are also similar, although they have somewhat different frequencies. These histologic and molecular similarities provide strong support for the use of parallel descriptive diagnostic terminology for neoplasms arising in the pancreas and the biliary tract. The revised WHO classification of exocrine pancreatic neoplasms accommodates most types of biliary tract neoplasms and provides a new basis for standardization of nomenclature.