Pancreatic tumours: molecular pathways implicated in ductal cancer are involved in ampullary but not in exocrine nonductal or endocrine tumorigenesis

Implication of the INK4a/ARF locus in gastroenteropancreatic neuroendocrine tumorigenesis

The INK4a/ARF locus on chromosome 9p21 is one of the important defenses against tumor development and engages both the Rb and the p53 tumor suppressor pathways through its capacity to encode two distinct proteins, p16(INK4a) and p14(ARF). Despite controversial reports, the body of present data suggests that tumor suppressors p16(INK4a) and p14(ARF) are targets of in-activation in GEP-NETs. Moreover, tumor type-specific aberrant p16(INK4a) silencing appears to be associated with advanced tumor stage and may function as a predictor of patients' outcome after surgical resection. Since conventional histological and biochemical assessment are limited with respect to predicting GEP-NET behavior or outcome, methylation profiles including INK4a/ARF might offer a tool to refine future diagnosis and therapeutic management of GEP-NET patients.

Molecular genetics of gastroenteropancreatic endocrine tumors

To elucidate the molecular background of sporadic gastroenteropancreatic endocrine tumors, several investigations into chromosomal alterations and allelic imbalances have identified several chromosomal regions of interest. These regions might harbor candidate genes important in tumor development and progression. However, only a small number of genes have been thoroughly analyzed, and only very few were shown to be altered in a substantial subset of tumors. Therefore, we are far from understanding the molecular mechanisms of tumor initiation and progression in gastroenteropancreatic endocrine tumors, although some "molecular patterns" are currently emerging. In this review, chromosomal alterations, that is, allelic losses and gene mutations, identified in gastroenteropancreatic endocrine tumors are briefly summarized. Molecular differences among various subtypes of gastroenteropancreatic endocrine tumors are highlighted in view of their role as indicators of separate genetic pathways.

Immunohistochemical analysis of adenocarcinoma of the small intestine: a tissue microarray study

BACKGROUND

Primary adenocarcinomas of the small intestine are rare, and the genetic mechanisms involved in their carcinogenesis remain unclear.

AIM

To examine the expression of candidate proteins in small intestinal adenocarcinomas by immunohistochemistry performed on tissue microarrays (TMAs).

METHODS

Twenty seven primary sporadic small intestinal adenocarcinomas were analysed. The TMA technique was validated by comparing immunohistochemical labelling of hMLH1 and hMSH2 on TMAs and the tissue sections they derived from. The expression of Smad4, hMSH6, beta catenin, and p53 was investigated and results compared with those obtained in 14 malignant ampullary tumours.

RESULTS

TMA technology with threefold redundancy adequately represented the immunohistochemical pattern of small intestinal adenocarcinomas. Loss of hMLH1 expression, but not hMSH2 or hMSH6, was seen in two of 27 small intestinal adenocarcinomas. All ampullary tumours showed nuclear staining for hMSH2 and hMSH6. One case showed lack of immunostaining for hMLH1. Smad4 expression was absent in five small intestinal adenocarcinomas and two ampullary tumours. Overexpression of p53 was detected in the nuclei of 14 of the 27 small intestinal adenocarcinomas, and five of the 14 ampullary tumours. Nuclear or cytoplasmic expression of beta catenin was present in all specimens.

CONCLUSION

Inactivation of the SMAD4/DPC4 gene seems to be involved in small intestinal adenocarcinoma tumorigenesis. Overexpression of p53 and abnormal expression of beta catenin are two common events, unlike the loss of expression of the DNA mismatch repair proteins (hMLH1, hMSH2, and hMSH6). The carcinogenetic process appears to be similar in small intestinal adenocarcinomas and malignant ampullary tumours.

A novel cell line and xenograft model of ampulla of Vater adenocarcinoma

Ampulla of Vater cancers (AVC) are of clinical relevance, as they represent more than one-third of patients undergoing surgery for pancreaticoduodenal malignancies and have a better prognosis than periampullary cancers of pancreaticobiliary origin. The availability of cellular models is crucial to perform cell biology and pharmacological studies and clarify the relationship between AVC and pancreatic and biliary cancers. Numerous cell lines are available for pancreatic and biliary adenocarcinomas, while only two have been reported recently for AVC. These were derived from a poor and a well-differentiated AVC, and both had wild-type K- ras and mutated p53. We report the establishment of a novel AVC cell line (AVC1) derived from a moderately differentiated cancer, having a mutated K- ras, wild-type p53, and methylated p16. Thus, our cell line adds to the spectrum of available in vitro models representative of the different morphological and molecular presentations of primary AVC. We further characterized AVC1 for the expression of relevant cell surface molecules and sensitivity to chemotherapeutic agents of common clinical use. It expresses MHC-I and CD95/Fas, while HLA-DR, CD40, CD80, CD86, MUC-1, MUC-2, and ICAM-1/CD54 are absent. It has a low to moderate sensitivity to both 5-FU and gemcitabine, at variance with much higher sensitivity displayed by two pancreatic ductal carcinoma cell lines. Lastly, AVC1 can be readily xenografted in immunodeficient mice, making it a suitable model for pre-clinical studies.

Loss of DPC4 expression and its correlation with clinicopathological parameters in pancreatic carcinoma

AIM: DPC4 is a tumor suppressor gene on chromosome 18q21.1 that has high mutant frequencies in pancreatic carcinogenesis. The purpose of this study was to investigate the role of DPC4 alterations in tumorigenesis and progression of pancreatic carcinomas.

METHODS: We studied the immunohistochemical markers of DPC4 in 34 adenocarcinomas and 16 nonmalignant specimens from the pancreas. The 16 nonmalignant specimens from the pancreas included 8 non-neoplastic cysts and 8 normal pancreatic tissues. The relationship between DPC4 alterations and various clinicopathological parameters was evaluated by chi-square test or Fisher’s exact test. Survivals were calculated using Kaplan-Meier method (by a log-rank test).

RESULTS: All the 16 nonmalignant cases of the pancreas showed expression of DPC4 gene. Loss of DPC4 expression was seen in 8 of 34(23.5%) pancreatic adenocarcinomas. The frequency of loss of DPC4 expression was higher in poorly differentiated adenocarcinoma (G3) than in well and moderately differentiated adenocarcinoma (G1 and G2) histologically (P = 0.037). Loss of DPC4 expression of the patients at TNM stage IV was also higher than that of the patients at TNM stages I, II and III (60.0% at stage IV, versus 14.3% at stage I, 18.2% at stage II, and 18.2% at stage III) (P = 0.223). The mean and median survival in patients with DPC4 expression was longer than those in patients with loss of DPC4 expression. Kaplan-Meier survival analysis demonstrated patients with DPC4 expression had a higher survival rate than patients with loss of DPC4 expression, but the difference did not reach statistical significance (P = 0.879).

CONCLUSION: This study suggests that DPC4 is involved in the development of pancreatic carcinoma and is a late event in pancreatic carcinogenesis, DPC4 expression may be a molecular prognostic marker for pancreatic carcinoma.

Trichostatin A, an inhibitor of histone deacetylases, strongly suppresses growth of pancreatic adenocarcinoma cells

In cells with an altered p53 gene, the expression of p21(WAF1/CIP1), a potent inhibitor of cyclin-dependent kinases, can be induced by histone deacetylase (HDAC) inhibitors via a p53-independent pathway, which may play a critical role in arrest of cell growth. Accordingly, HDAC inhibitors such as trichostatin A (TSA) have potential utility in pancreatic cancer, as most of these tumors possess mutations in p53, which in fact is the main cause of chemoresistance to 5-fluorouracil. We have analyzed the effect of TSA on the proliferation of nine pancreatic adenocarcinoma cell lines, all containing a mutated p53 gene. TSA strongly inhibited the cellular growth of all these cell lines at submicromolar concentrations. The cellular mechanisms underlying this effect consisted of cell cycle arrest at the G2 phase and apoptotic cell death. The expression of p21(WAF1/CIP1) normally induced at the transcriptional level by p53 was also strongly activated by TSA. These findings suggest that inhibitors of HDAC may represent a novel therapeutic strategy for treatment of pancreatic cancer.

SEL1L expression in pancreatic adenocarcinoma parallels SMAD4 expression and delays tumor growth in vitro and in vivo

Recent data suggest that SEL1L may play an important role in pancreatic carcinoma, similar to breast cancer, where the expression of SEL1L has been associated with a reduction in both proliferative activity in vitro and clinical tumor aggressiveness. To investigate this possibility, we examined the expression of Sel1L in a series of primary pancreatic carcinomas by immunohistochemistry and characterized the effects of Sel1L overexpression both in vitro and in vivo. In 74 pancreatic cancers analysed, 36% lacked Sel1L expression, although there was no significant correlation between the expression of Sel1L and any clinicopathologic parameter, including survival. However, immunohistochemical reactivity for Sel1L and Dpc4/Smad4 was concordant in 69% of cases (chi(2) test P&<0.004). Overexpression of SEL1L in stably transfected pancreatic cancer cells caused both a decrease in clonogenicity and anchorage-independent growth as well as a significant increase in the levels of activin A and SMAD4. When implanted in nude mice, Suit-2-SEL1L-overexpressing clones displayed a considerably reduced rate of tumor growth. Thus, it can be hypothesized that Sel1L plays an important function in the growth and aggressiveness of pancreatic carcinoma. Moreover, our data provide evidence that SEL1L has an impact on the expression of genes involved in regulation of cellular growth, possibly through the TGF-beta signaling pathway.

The genetics of pancreatic cancer

The genetic basis for invasive and preoneoplastic neoplasms of the exocrine and endocrine pancreas has been the subject of a number of investigations in recent years. The purpose of this paper was to briefly review and summarize the pertinent findings. High frequency changes associated with pancreatic adenocarcinomas include mutations of the k-ras oncogene, and inactivating alterations of the p53, p16, and DPC4 tumor suppressor genes. Hereditary syndromes that have a known predisposition for pancreatic adenocarcinoma development include hereditary pancreatitis, familial atypical multiple mole melanoma (FAMM) syndrome, Peutz-Jeghers syndrome, familial breast cancer (BRCA-2), hereditary nonpolyposis colorectal cancer syndrome (HNPCC), and Li-Fraumeni syndrome. The underlying genetic defects have been identified and are currently being studied. Germline mutations of the men-1 gene are responsible for the MEN-1 syndrome, known to be associated with pancreatic endocrine tumors. It appears that somatic mutations of the gene are present in at least a subset of sporadic tumors. In addition, alterations in the Rb/p16 pathway appear to be commonly associated with pancreatic endocrine tumors. Further characterization of pancreatic tumors will result in a better understanding of the cellular pathways involved in pancreatic tumorigenesis and holds promise to identify targets for novel diagnostic and therapeutic strategies.

Motility analysis of pancreatic adenocarcinoma cells reveals a role for the atypical zeta isoform of protein kinase C in cancer cell movement

The acquisition of an invasive and metastatic phenotype is accompanied by profound alterations of intracellular mechanisms controlling cell movement. Analysis of quantitative parameters of cell motility in cancer cells may help in the identification of intracellular signaling events determining invasion and metastasis. Here we developed a novel procedure of quantification of cell motility based on time-lapse video microscopy and digital image analysis. Three kinetic parameters, including area change, plasma membrane remodeling, and speed of linear movement, are quantified and combined in one single, time-normalized value we defined motility score (MS). Through calculation of the MS for various human pancreatic adenocarcinoma cell subclones, we identified clones characterized by low or high spontaneous motility in vitro. Analysis of the signaling mechanisms involved in the regulation of pancreatic adenocarcinoma cell motility showed that the atypical zeta isozyme of the serine-threonine protein kinase C (PKC) plays a critical role in maintaining a high MS in motile subclones, as demonstrated by the inhibitory effect of cell permeable peptides with sequence corresponding to the pseudosubstrate inhibitory region of the atypical zeta PKC. Other PKC isozymes, either classic or novel, seem not involved. Furthermore, biochemical analysis showed that in motile cells, zeta PKC is constitutively associated with the plasma membrane, whereas in nonmotile cells, zeta PKC is totally excluded from the plasma membrane. These data suggest that the disregulation of the function of atypical zeta PKC might be involved in the acquisition of an invasive and metastatic phenotype in pancreatic adenocarcinoma cells.

Loss of Stk11/Lkb1 expression in pancreatic and biliary neoplasms

We have documented previously somatic mutations of STK11/LKB11, the gene responsible for Peutz-Jeghers syndrome (PJS), in a small proportion of sporadic pancreatic adenocarcinomas, intraductal papillary mucinous neoplasms (IPMNs), and biliary adenocarcinomas. In this report, we characterize the expression of Stk11, the protein product of the STK11 gene, in a larger series of pancreatic and biliary neoplasms. First, the specificity of the Stk11 antibody was established in 23 neoplasms (22 IPMNs and 1 biliary adenocarcinoma) with known STK11 gene status. Complete absence of labeling was seen in the neoplastic cells of 3 of the 3 (100%) cases with previously documented biallelic inactivation of the STK11 gene, whereas 16 of the 20 (80%) IPMNs, presumably with at least one wild-type STK11 gene, retained Stk11 expression in the neoplastic cells. The marked decrease or absence of Stk11 expression in four neoplasms with wild-type STK11 suggests that additional mechanisms may account for the lack of Stk11 expression. Subsequently, to further evaluate Stk11 expression in pancreatic and biliary neoplasms, tissue microarrays (TMAs) were constructed from a series of nearly 100 ductal adenocarcinomas and biliary neoplasms. Stk11 expression was lost in 4 of the 56 (7%) pancreatic adenocarcinomas and 1 of the 38 (2.6%) biliary cancers by immunohistochemistry; the absence of labeling was confirmed by repeated immunohistochemical labeling of complete tissue sections for the same cases. Thus, Stk11 expression is abrogated in a small proportion of pancreatic and biliary neoplasms. The inactivation of Stk11 in 27% (6/22) of IPMNs versus 7% (4/56) of pancreatic adenocarcinomas suggests genetic disparities in the pathogenesis of these closely related neoplasms. Immunohistochemical analysis for Stk11 expression may be a valid surrogate for genetic analysis of STK11 gene mutations in cancers.

[Pathogenesis and histomorphology of ampullary carcinomas and their precursor lesions. Review and individual findings]

Most adenomas and carcinomas of small intestine and extrahepatic bile ducts arise in the region of Vater's papilla. In FAP it is the main location for carcinomas after proctocolectomy. In many cases symptoms due to stenosis lead to diagnosis in an early tumor stage. In about 80% curative intended resection is possible. Operability is the most relevant prognostic factor. Inflammatory changes, fibrosis, regeneratory changes after endoscopic manipulation, hyperplasia, preneoplastic lesions close to carcinoma, deeply sited carcinomas under protruded, non-neoplastic duodenal mucosa make the diagnosis difficult on biopsy material. Histologically, intestinal type adenocarcinoma, pancreatobiliary type adenocarcinoma, undifferentiated carcinomas and unusual types can be differentiated. In our own series comprising 45 resected ampullary carcinomas 6 from 10 intestinal type adenocarcinomas, and 4 carcinomas of unusual types expressed the immunohistochemical marker profile of intestinal mucosa (keratin 7-, keratin 20+, MUC2+). 17 from 21 pancreatobiliary type adenocarcinomas, 4 undifferentiated carcinomas, as well as 3 papillary carcinomas showed the immunohistochemical profile of pancreaticobiliary duct mucosa (keratin 7+, keratin 20-, MUC2-). 3 invasive carcinomas which were negative for these markers, showed one of these characteristic marker-combinations in non-invasive adenomatous parts. These findings support the concept of histogenetically different ampullary carcinomas which are developing from the intestinal or from the pancreaticobiliary type mucosa of Vater's papilla. Molecular alterations in ampullary carcinomas are similar to those of colorectal as well as pancreatic carcinomas, although they appear in different frequencies. In future studies molecular alterations in ampullary carcinomas should be correlated closely with the different histologic tumor types. The histologic classification should reflect consequently the histogenesis of ampullary tumors from the two different types of papillary mucosa.

Role of the DPC4 tumor suppressor gene in adenocarcinoma of the ampulla of Vater: analysis of 140 cases

The K-ras oncogene is activated in approximately 90% of pancreatic adenocarcinomas, and the DPC4 (MADH4/SMAD4) tumor suppressor gene is inactivated in approximately 55% of pancreatic adenocarcinomas. The contributions of these genetic alterations to the development of adenocarcinoma of the ampulla of Vater have not been fully established. One hundred forty surgically resected ampullary adenocarcinomas (76 with associated adenomas with high-grade dysplasia) were immunohistochemically labeled for the DPC4 gene product, and in 85 cases the results were correlated with the status of the K-ras oncogene from previously reported data. The results were correlated with clinical outcome and with other pathologic predictors of prognosis. Complete loss of Dpc4 labeling was identified in 34% (95% confidence interval [CI]: 26%, 43%) of the invasive carcinomas and in none (upper 95% CI: 6%) of the associated adenomas. Focal loss of Dpc4 was seen in three (4%; 95% CI: 1%, 14%) of the areas of high-grade dysplasia. Complete loss of Dpc4 expression was seen in 28/77 intestinal-type tumors, in 17/46 pancreaticobiliary-type tumors, and in 0/10 colloid carcinomas. Activating point mutations in the K-ras gene were identified in 40% of the invasive cancers. There was no correlation between K-ras gene mutations and Dpc4 expression and no correlation between these variables and survival. The overall 5-year survival rate was 38%. Lymph node metastases were associated with shorter survival (P =.03). Loss of Dpc4 expression occurs in approximately one third of invasive ampullary cancers but is not seen in adenomas; thus, loss of Dpc4 expression occurs late in ampullary carcinogenesis. Although ampullary and pancreatic adenocarcinomas share histologic and molecular features, ampullary carcinomas are less likely to show loss of Dpc4 expression or K-ras gene mutations.

Methylation status of p14ARF and p16INK4a as detected in pancreatic secretions

The clinical management of pancreatic disease is often hampered by a lack of tissue diagnosis. Endoscopic pancreatography offers the opportunity to investigate exfoliated cells. However, the significance of mere cytological investigation is compromised by an insufficient sensitivity. The evaluation of the molecular background of carcinogenesis hopefully is capable of providing more sensitive diagnostic markers. The p16INK4a-/retinoblastoma tumour-suppressive pathway has been shown to be involved in the development of near to all pancreatic neoplasms. p14ARF is another tumour suppressor located in the immediate neighbourhood of p16INK4a. Promoter methylation has been demonstrated to be a major inactivating mechanism of both genes. We sought to further evaluate the role of the gene locus INK4a methylation status in the endoscopic differentiation of chronic inflammatory and neoplastic pancreatic disease. Pancreatic fluid specimens of 61 patients with either pancreatic carcinoma (PCA: 39), chronic pancreatitis (CP: 16) or a normal pancreatogram (NAD: 6) were retrieved. In order to detect methylation of either the p14ARF or the p16INK4a promoter a methylation-specific PCR protocol was applied. While 19 out of 39 patients with PCA showed p16 promoter methylation (49%), none of the 16 patients with CP revealed p16 promoter methylation. p14ARF methylation was found in a lower percentage of PCA specimens and in none of the samples of patients with CP. These results suggest a specific significance of INK4a for the development of malignant pancreatic disease. Our data further indicate a potential role for INK4a methylation as a diagnostic marker in the endoscopic differentiation of benign and malignant pancreatic disease.

Genetic abnormalities in pancreatic cancer

The incidence and mortality of pancreatic adenocarcinoma are nearly coincident having a five-year survival of less than 5%. Enormous advances have been made in our knowledge of the molecular alterations commonly present in ductal cancer and other pancreatic malignancies. One significant outcome of these studies is the recognition that common ductal cancers have a distinct molecular fingerprint compared to other nonductal or endocrine tumors. Ductal carcinomas typically show alteration of K-ras, p53, p16INK4, DPC4 and FHIT, while other pancreatic tumor types show different aberrations. Among those tumors arising from the exocrine pancreas, only ampullary cancers have a molecular fingerprint that may involve some of the same genes most frequently altered in common ductal cancers. Significant molecular heterogeneity also exists among pancreatic endocrine tumors. Nonfunctioning pancreatic endocrine tumors have frequent mutations in MEN-1 and may be further subdivided into two clinically relevant subgroups based on the amount of chromosomal alterations. The present review will provide a brief overview of the genetic alterations that have been identified in the various subgroups of pancreatic tumors. These results have important implications for the development of genetic screening tests, early diagnosis, and prognostic genetic markers.

Absence of mutations in the transforming growth factor-beta inducible early gene 1, TIEG1, in pancreatic cancer

Pancreatic cancers frequently have defects in components of the transforming growth factor-beta (TGF-beta) signaling pathway. TIEG1 (TGF-beta inducible early gene) is a recently characterized transcription factor regulated by TGF-beta that induces apoptosis when overexpressed in pancreatic adenocarcinoma cell lines. Alterations on chromosome 8q, where TIEG1 is located, are also relatively frequent in pancreatic cancers. To determine if TIEG1 may be involved in the tumorigenesis of pancreatic cancer, we performed mutational screening of this gene in 22 pancreatic cancer cell lines. No sequence alterations were observed. Reverse transcription-polymerase chain reaction analysis was also performed to rule out the possibility that the expression of the gene is altered by genetic events other than mutation. Likewise, no alterations in expression were found. Thus, an essential role of TIEG1 in pancreatic cancer can be excluded.

Molecular insights into gastrointestinal neuroendocrine tumours: importance and recent advances

A subset of gastrointestinal neuroendocrine tumours (carcinoids and pancreatic endocrine tumours) show aggressive growth. Early identification of this subset is essential for management; however, clinical, laboratory and histologic features frequently fail to achieve this. Currently, there is an increased understanding of the molecular pathogenesis/changes in neuroendocrine tumours and this may identify important prognostic factors and possibly, new treatments. Recent findings and progress in this area are briefly reviewed in this article.

Review of the clinical, histological, and molecular aspects of pancreatic endocrine neoplasms

Pancreatic endocrine neoplasms (PENs) are rare tumors, and little is known about their genetic and chromosomal alterations. Elucidation of the molecular events involved in PEN carcinogenesis has been hindered by the fact that PENs have been considered a single disease entity. The emergence of novel molecular characterization strategies has, however, made it apparent that these lesions exhibit diverse molecular fingerprints, which will facilitate the precise delineation of PEN prognosis, histopathology, and carcinogenesis.

Expression profiling of microdissected pancreatic adenocarcinomas

Pancreatic ductal adenocarcinoma is characterized by a paucity of neoplastic cells embedded in a densely desmoplastic stroma. Therefore, laser capture microdissection was performed to obtain homogeneous populations of normal and neoplastic ductal cells. These were subjected to a comparative study of gene expression utilizing human cDNA arrays. A variety of dysregulated genes were identified, comprising cell cycle and growth regulators, invasion regulators, signalling and developmental molecules. In addition to genes already found to be overexpressed in pancreatic cancer, such as TIMP1, MMP7, CD59, rhoC and NDKA, we present evidence to implicate genes which have not previously been reported in this tumour type. These include the overexpressed genes ABL2, Notch4 and SOD1, as well as XRCC1, a DNA repair gene whose transcript was found downregulated. Quantitative real-time RT-PCR (QRT-PCR) was employed to confirm differential expression of ABL2, Notch4 and SOD1 and immunohistochemical analysis was used to verify decreased protein expression of XRCC1 using a custom-built pancreatic tissue array. Combining microarray-derived gene expression profiles of pure pancreatic cell populations, QRT-PCR and pancreas-specific tissue arrays therefore proved to be highly informative in elucidating the molecular pathology of this highly malignant tumour type.

Multiple loss of heterozygosity without K-ras mutation identified by molecular analysis on fine-needle aspiration cytology specimen of acinar cell carcinoma of pancreas

Fine-needle aspiration diagnosis of pancreatic acinar cell carcinoma (PAC) is challenging. Typically, the cytologic findings in PAC are described as a cellular population of loosely cohesive clusters and single neoplastic cells. The individual cells have granular cytoplasm, uniform nuclei, a fine chromatin pattern, and occasional prominent nucleoli. These features are suggestive of PAC but not diagnostic. We illustrate a case in which the combination of cytopathologic findings, clinical information, and molecular analysis enabled us to arrive at the diagnosis of PAC. Although the cytomorphologic features alone were not specific, the presence of a markedly elevated serum lipase level, cutaneous lesions of fat necrosis, and loss of heterozygosity at 1p, 5q25 at the APC locus, 9p21 at the p16 locus, and 17p13 at the p53 locus were essential in excluding the main differential diagnostic entities including pancreatic ductal carcinoma, pancreatic endocrine tumor, and pancreatoblastoma.

Aberrant methylation of CpG islands in intraductal papillary mucinous neoplasms of the pancreas

BACKGROUND & AIMS

The functional abrogation of several tumor suppressor genes, including p16, DPC4, and p53, is a major mechanism underlying pancreatic ductal carcinogenesis. However, mutational inactivation of these genes is relatively uncommon in intraductal papillary mucinous neoplasms (IPMNs) of the pancreas. We hypothesized that an alternative mechanism for gene inactivation (notably, transcriptional silencing by promoter methylation) could be important in the pathogenesis of IPMNs.

METHODS

Using methylation-specific polymerase chain reaction, we analyzed the methylation status of 7 CpG islands previously identified as aberrantly methylated in pancreatic adenocarcinoma (including preproenkephalin [ppENK], p16, and thrombospondin 1) in 51 IPMNs of different histologic grades. The relationship between methylation status and expression was evaluated using reverse-transcription polymerase chain reaction for ppENK and immunohistochemistry for p16.

RESULTS

We found that more than 80% of the IPMNs exhibited hypermethylation of at least one of these CpG islands. Hypermethylation of ppENK and p16 was detected at a significant higher frequency in high-grade (in situ carcinoma) IPMNs than in low-grade (adenoma/borderline) IPMNs (ppENK, 82% vs. 28%, P = 0.0002; p16, 21% vs. 0%, P = 0.04). Furthermore, the average number of methylated loci was significantly higher in high-grade IPMNs than in low-grade IPMNs (2.4 vs. 0.9; P = 0.0008). Aberrant methylation of ppENK and p16 was associated with loss of expression.

CONCLUSIONS

These results suggest that de novo methylation of multiple CpG islands is one of the critical pathways that contributes to the malignant progression of IPMNs.

Characterization of gene expression profiles in intraductal papillary-mucinous tumors of the pancreas

The molecular pathology of precursor lesions leading to invasive pancreatic ductal adenocarcinomas remains relatively unknown. We have applied cDNA microarray analysis to characterize gene expression profiles in a series of intraductal papillary-mucinous tumors (IPMTs) of the pancreas, which represents one of the alternative routes of intraepithelial progression to full malignancy in the pancreatic duct system. Using a cDNA microarray containing 4992 human genes, we screened a total of 13 IPMTs including nine noninvasive and four invasive cases. Expression change in more than half of the tumors was observed for 120 genes, ie, 62 up-regulated and 58 down-regulated genes. Some of the up-regulated genes in this study have been previously described in classical pancreatic carcinomas such as lipocalin 2, galectin 3, claudin 4, and cathepsin E. The most highly up-regulated genes in IPMTs corresponded to three members of the trefoil factor family (TFF1, TFF2, and TFF3). Immunohistochemistry performed on five genes found to be differentially expressed at the RNA level (TFF1, TFF2, TFF3, lipocalin 2, and galectin 3) showed a good concordance between transcript level and protein abundance, except for TFF2. Hierarchical clustering organized the cases according to the dysplastic and invasive phenotype of theIPMTs. This analysis has permitted us to implicate several genes (caveolin 1, glypican 1, growth arrest-specific 6 protein, cysteine-rich angiogenic inducer 61) in tumor progression. The observation that several genes are differentially expressed both in IPMTs and pancreatic carcinomas suggests that they may be involved at an early stage of pancreatic carcinogenesis.

Solid-pseudopapillary tumors of the pancreas are genetically distinct from pancreatic ductal adenocarcinomas and almost always harbor beta-catenin mutations

Solid-pseudopapillary tumors (SPTs) are unusual pancreatic neoplasms of low malignant potential that most frequently affect young women. Genetic events contributing to the development of SPTs are unknown. Whereas the more common ductal adenocarcinomas of the pancreas essentially never harbor beta-catenin or APC gene mutations, we have recently identified alterations of the APC/beta-catenin pathway in other nonductal pancreatic neoplasms including pancreatoblastomas and acinar cell carcinomas. We analyzed a series of 20 SPTs for somatic alterations of the APC/beta-catenin pathway using immunohistochemistry for beta-catenin protein accumulation, direct DNA sequencing of beta-catenin exon 3, and direct DNA sequencing of the mutation cluster region in exon 15 of the APC gene in those SPTs that did not harbor beta-catenin mutations. Immunohistochemical labeling for cyclin D1 was performed to evaluate the overexpression of this cell-cycle protein as one of the putative downstream effectors of beta-catenin dysregulation. In addition, we analyzed the SPTs for genetic alterations commonly found in pancreatic ductal adenocarcinomas, including mutations in the K-ras oncogene and p53 and DPC4 tumor suppressor genes, using direct DNA sequencing of K-ras and immunostaining for p53 and Dpc4. Almost all SPTs harbored alterations in the APC/beta-catenin pathway. Nuclear accumulation of beta-catenin protein was present in 95% (19 of 20), and activating beta-catenin oncogene mutations were identified in 90% (18 of 20) of the SPTs. Seventy-four percent (14 of 19) showed overexpression of cyclin D1, ranging from 10 to 70% of tumor nuclei. In contrast, no K-ras mutations were present in any of the 20 SPTs, and Dpc4 expression was intact in all 16 SPTs for which immunohistochemical labeling was successful. Overexpression of p53 was limited to only 3 of 19 (15.8%) SPTs. These results emphasize the two distinct, divergent genetic pathways of neoplastic progression in pancreatic ductal and nonductal neoplasms.

Sex chromosome anomalies in pancreatic endocrine tumors

We have investigated the status of sex chromosomes in 40 pancreatic endocrine tumors (PETs) using 2 complementary techniques: microsatellite and interphase FISH analysis. Twenty-five tumors were from female and 15 from male patients and included 31 nonfunctioning and 9 functioning PET (6 insulinomas, 2 glucagonomas and 1 VIPoma). Microsatellite and FISH analysis showed concordant results in all cases. PETs from females showed frequent loss of chromosome X (40%) whereas PETs from males showed relatively frequent loss of chromosome Y (36%) but never loss of the X chromosome. Statistical analysis showed significant association of sex chromosome loss with metastases (Spearman correlation test, r = 0.5, p < 0.001), local invasion (r = 0.33, p < 0.05) and high proliferation rate measured as Ki-67 index with a 5% cut-off (r = 0.42, p < 0.02). The analysis also showed that local invasion and metastases were highly correlated (r = 0.86). Multivariate survival analysis was therefore carried out including local invasion and loss of sex chromosomes. The presence of local invasion increased the risk of death almost 9 times whereas sex chromosome loss was an independent variable associated with a shorter survival period and an increased risk of death of approximately 4-fold.

Genetic and immunohistochemical analysis of pancreatic acinar cell carcinoma: frequent allelic loss on chromosome 11p and alterations in the APC/beta-catenin pathway

Acinar cell carcinomas (ACCs) are rare malignant tumors of the exocrine pancreas. The specific molecular alterations that characterize ACCs have not yet been elucidated. ACCs are morphologically and genetically distinct from the more common pancreatic ductal adenocarcinomas. Instead, the morphological, immunohistochemical, and clinical features of ACCs overlap with those of another rare pancreatic neoplasm, pancreatoblastoma. We have recently demonstrated a high frequency of allelic loss on chromosome arm 11p and mutations in the APC/beta-catenin pathway in pancreatoblastomas, suggesting that similar alterations might also play a role in the pathogenesis of some ACCs. We analyzed a series of 21 ACCs for somatic alterations in the APC/beta-catenin pathway and for allelic loss on chromosome 11p. In addition, we evaluated the ACCs for alterations in p53 and Dpc4 expression using immunohistochemistry, and for microsatellite instability (MSI) using polymerase chain amplification of a panel of microsatellite markers. Allelic loss on chromosome 11p was the most common genetic alteration in ACCs, present in 50% (6 of 12 informative cases). Molecular alterations in the APC/beta-catenin pathway were detected in 23.5% (4 of 17) of the carcinomas, including one ACC with an activating mutation of the beta-catenin oncogene and three ACCs with truncating APC mutations. One ACC (1 of 13, 7.6%) showed allelic shifts in four of the five markers tested (MSI-high), two (15.4%) showed an allelic shift in only one of the five markers tested (MSI-low), and no shifts were detected in the remaining 10 cases. The MSI-high ACC showed medullary histological features. In contrast, no loss of Dpc4 protein expression or p53 accumulation was detected. These results indicate that ACCs are genetically distinct from pancreatic ductal adenocarcinomas, but some cases contain genetic alterations common to histologically similar pancreatoblastomas.

STK11/LKB1 Peutz-Jeghers gene inactivation in intraductal papillary-mucinous neoplasms of the pancreas

Despite the growing awareness of intraductal papillary-mucinous neoplasms (IPMNs) of the pancreas among clinicians, the molecular features of IPMNs have not been well characterized. Previous reports suggest that inactivation of the STK11/LKB1, a tumor-suppressor gene responsible for Peutz-Jeghers syndrome (PJS), plays a role in the pathogenesis of gastrointestinal hamartomas as well as several cancers, including pancreatic adenocarcinoma. Using polymerase chain reaction amplification of five microsatellite markers from the 19p13.3 region harboring the STK11/LKB1 gene, we analyzed DNA from 22 IPMNs for loss of heterozygosity (LOH). LOH at 19p13.3 was identified in 2 of 2 (100%) IPMNs from patients with PJS and 5 of 20 (25%) from patients lacking features of PJS (7 of 22, 32% overall). Sequencing analysis of the STK11/LKB1 gene in these IPMNs with LOH revealed a germline mutation in one IPMN that arose in a patient with PJS and a somatic mutation in 1 of the 20 sporadic IPMNs. None of the 22 IPMNs showed hypermethylation of the STK11/LKB1 gene. These results suggest that the STK11/LKB1 gene is involved in the pathogenesis of some IPMNs.

Distinctive molecular genetic alterations in sporadic and familial adenomatous polyposis-associated pancreatoblastomas : frequent alterations in the APC/beta-catenin pathway and chromosome 11p

Pancreatoblastomas are unusual malignant neoplasms of the pediatric pancreas that may also rarely affect adults. The molecular pathogenesis of pancreatoblastomas is unknown. They are clinicopathologically distinct from adult pancreatic ductal adenocarcinomas, but their occasional occurrence in patients with Beckwith-Wiedemann syndrome and the case presented here of a pancreatoblastoma in an adult patient with familial adenomatous polyposis (FAP) suggests that they might bear a genetic similarity to other infantile embryonal tumors such as hepatoblastomas. We analyzed a series of nine pancreatoblastomas for mutations common to other embryonal malignancies including somatic alterations in the adenomatous polyposis coli (APC)/beta-catenin pathway and chromosome 11p, using immunohistochemistry for beta-catenin, 5q and 11p allelic loss assays, and direct DNA sequencing of exon 3 of the beta-catenin gene and the mutation cluster region of the APC gene. In addition, we analyzed the pancreatoblastomas for alterations found in adult-type pancreatic ductal adenocarcinomas including mutations in the K-ras oncogene and the p53 and DPC4 tumor suppressor genes, using direct DNA sequencing of exon 1 of K-ras and immunohistochemistry for p53 and Dpc4. Allelic loss on chromosome 11p was the most common genetic alteration in pancreatoblastomas, present in 86% (six of seven informative cases). Molecular alterations in the APC/beta-catenin pathway were detected in 67% (six of nine), including five neoplasms with activating mutations of the beta-catenin oncogene and the one FAP-associated tumor with biallelic APC inactivation (germline truncating mutation combined with loss of the wild-type allele); seven neoplasms showed abnormal nuclear accumulation of beta-catenin protein. In contrast, loss of Dpc4 protein expression was present in only two cases (one diffuse and one focal), and no alterations in the K-ras gene or p53 expression were detected. Our findings indicate that pancreatoblastomas are genetically distinct from the more common pancreatic ductal adenocarcinomas, but bear a close molecular pathogenesis to hepatoblastomas. In addition, pancreatoblastoma may represent an extracolonic manifestation of FAP.

Role of disease-causing genes in sporadic pancreatic endocrine tumors: MEN1 and VHL

Pancreatic endocrine tumors (PETs) occur in association with multiple endocrine neoplasia type 1 (MEN1) and von Hippel-Lindau (VHL) syndromes caused by germline alterations in MEN1 and VHL, respectively. It is thus expected that these genes will also be altered in a proportion of sporadic PETs. Indeed, MEN1 is altered in about 25% of nonfamilial PETs, although no mutations have been found in VHL. For all clinical subtypes, the frequency of allelic loss on chromosome arm 11q mirrors observed mutational frequencies, with the exception of nonfunctional tumors (NF-PETs), in which mutations have been reported in only 8% of cases. As allelic loss on 11q is the most frequent event found in these neoplasms, this low frequency is somewhat puzzling, particularly in light of the fact that most MEN1-associated PETs are nonfunctioning. To clarify the role of these genes in sporadic PETs, we analyzed 31 sporadic NF-PETs, nine insulinomas, and one VIPoma for alterations in MEN1 and VHL. As somatic mutations were observed in eight (26%) of the NF tumors and in one insulinoma, it would therefore appear unlikely that an additional tumor suppressor gene related to sporadic PET pathogenesis is located on 11q. One insulinoma also had a somatic mutation in VHL, and thus this gene may also be altered in these neoplasms, albeit in a small proportion of cases.