Robb E. Wilentz

Solid-Pseudopapillary Tumors of the Pancreas Are Genetically Distinct from Pancreatic Ductal Adenocarcinomas and Almost Always Harbor β-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.

Genetic progression in the pancreatic ducts

The genetic progression described by Yamano et al in this issue of The American Journal of Pathology helps establish a progression model for pancreatic ductal carcinoma. This progression model has a number of important implications for the classification of lesions in the pancreas and for the future early detection and chemoprevention of pancreatic carcinoma.

Telomere shortening is nearly universal in pancreatic intraepithelial neoplasia.

A multistep model of carcinogenesis has recently been proposed for pancreatic ductal adenocarcinomas. In this model, noninvasive precursor lesions in the pancreatic ductules accumulate genetic alterations in cancer-associated genes eventually leading to the development of an invasive cancer. The nomenclature for these precursor lesions has been standardized as pancreatic intraepithelial neoplasia or PanIN. Despite the substantial advances made in understanding the biology of invasive pancreatic adenocarcinomas, little is known about the initiating genetic events in the pancreatic ductal epithelium that facilitates its progression to cancer. Telomeres are distinctive structures at the ends of chromosomes that protect against chromosomal breakage-fusion-bridge cycles in dividing cells. Critically shortened telomeres can cause chromosomal instability, a sine qua non of most human epithelial cancers. Although evidence for telomeric dysfunction has been demonstrated in invasive pancreatic cancer, the onset of this phenomenon has not been elucidated in the context of noninvasive precursor lesions. We used a recently described in situ hybridization technique in archival samples (Meeker AK, Gage WR, Hicks JL, Simon I, Coffman JR, Platz EA, March GE, De Marzo AM: Telomere length assessment in human archival tissues: combined telomere fluorescence in situ hybridization and immunostaining. American Journal of Pathology 2002, 160:1259-1268) for assessment of telomere length in tissue microarrays containing a variety of noninvasive pancreatic ductal lesions. These included 82 PanIN lesions of all histological grades (24 PanIN-1A, 23 PanIN-1B, 24 PanIN-2, and 11 PanIN-3) that were selected from pancreatectomy specimens for either adenocarcinoma or chronic pancreatitis. Telomere fluorescence intensities in PanIN lesions were compared with adjacent normal pancreatic ductal epithelium and acini (62 of 82 lesions, 76%), or with stromal fibroblasts and islets of Langerhans (20 of 82 lesions, 24%). Telomere signals were strikingly reduced in 79 (96%) of 82 PanINs compared to adjacent normal structures. Notably, even PanIN-1A, the earliest putative precursor lesion, demonstrated a dramatic reduction of telomere fluorescence intensity in 21 (91%) of 23 foci examined. In chronic pancreatitis, reduction of telomere signal was observed in all PanIN lesions, whereas atrophic and inflammatory ductal lesions retained normal telomere length. Telomere fluorescence intensity in PanIN lesions did not correlate with proliferation measured by quantitative Ki-67-labeling index or topoisomerase IIalpha expression. Thus, telomere shortening is by far the most common early genetic abnormality recognized to date in the progression model of pancreatic adenocarcinomas. Telomeres may be an essential gatekeeper for maintaining chromosomal integrity, and thus, normal cellular physiology in pancreatic ductal epithelium. A critical shortening of telomere length in PanINs may predispose these noninvasive ductal lesions to accumulate progressive chromosomal abnormalities and to develop toward the stage of invasive carcinoma.

Pancreaticoduodenectomy (Whipple resections) in patients without malignancy: Are they all 'chronic pancreatitis'?

Pancreaticoduodenectomy (Whipple resection) has evolved into a safe procedure in major high-volume medical centers for the treatment of pancreatic adenocarcinoma and refractory chronic pancreatitis. However, some Whipple resections performed for a clinical suspicion of malignancy reveal only benign disease on pathologic examination. We evaluated the frequency of such Whipple resections without tumor in a large series of pancreaticoduodenectomies and classified the diverse pancreatic and biliary tract diseases present in these specimens. Of 442 Whipple resections performed during 1999–2001, 47 (10.6%) were negative for neoplastic disease and, in 40 cases, had been performed for a clinical suspicion of malignancy. Most Whipple resections revealed benign pancreatic disease, including 8 (17%) alcohol-associated chronic pancreatitis, 4 (8.5%) gallstone-associated pancreatitis, 1 (2.1%) pancreas divisum, 6 (12.8%) “ordinary” chronic pancreatitis of unknown etiology, and 11 (23.4%) lymphoplasmacytic sclerosing pancreatitis. In particular, patients with lymphoplasmacytic sclerosing pancreatitis were all thought to harbor malignancy, whereas only 13 of 19 (68.4%) of Whipple resections showing histologically “ordinary” forms of chronic pancreatitis were performed for a clinical suspicion of malignancy. Benign biliary tract disease, including three cases of primary sclerosing cholangitis, two cases of choledocholithiasis-associated chronic biliary tract disease, and four fibroinflammatory strictures isolated to the intrapancreatic common bile duct, was a common etiology for clinically suspicious Whipple resections (22.5% of cases). Pancreatic intraepithelial neoplasia (PanIN) was a common finding among all pancreata, whether involved by pancreatitis or histologically normal. Overall, PanIN 1A/1B was present in 68.1%, PanIN 2 in 40.4%, and PanIN 3 in just 2.1%. These findings indicate that “benign but clinically suspicious” Whipple resections are relatively common in high-volume centers (9.2%) and reveal a diverse group of clinicopathologically distinctive pancreatic and biliary tract disease.

Immunohistochemical Labeling for Dpc4 Mirrors Genetic Status in Pancreatic Adenocarcinomas: A New Marker of DPC4 Inactivation

DPC4 (MADH4, SMAD4) is a tumor suppressor gene inactivated by allelic loss in approximately 55% of pancreatic adenocarcinomas. Unfortunately, it can be technically very difficult to detect the inactivation of DPC4 at the genetic level because genetic analyses require the microdissection of relatively pure samples of neoplastic and normal tissues. This is especially true for pancreatic adenocarcinomas, which elicit vigorous, non-neoplastic, stromal responses. Immunohistochemical labeling can overcome this hurdle because it preserves morphological information. We therefore studied the expression of the DPC4 gene product in 46 cancers, including 5 cancer cell lines by Western blot analysis and 41 primary periampullary adenocarcinomas by immunohistochemistry. The status of exons 1-11 of the DPC4 gene in all 46 of the cancers had been previously characterized at the molecular level, allowing us to correlate Dpc4 expression directly with gene status. Three cell lines had wild-type DPC4 genes, and Dpc4 expression was detected in all three by Western blot. The two cell lines with homozygously deleted DPC4 genes did not show Dpc4 protein by Western blot analysis. Immunohistochemical labeling revealed that 17 (94%) of the 18 primary adenocarcinomas with wild-type DPC4 genes expressed the DPC4 gene product, whereas 21 (91%) of 23 primary adenocarcinomas with inactivated DPC4 genes did not. Cases in which there was discordance between the immunohistochemical labeling and the genetic analyses were reanalyzed genetically, and we identified a deletion in exon 0 of DPC4 in one of these cases. This is the first report of a mutation in exon 0 of DPC4 in a pancreatic cancer. The contrast between the strong expression of Dpc4 by normal tissues and the loss of expression in the carcinomas was highlighted in several cases in which an infiltrating cancer was identified growing into a benign duct. These observations suggest that immunohistochemical labeling for the DPC4 gene product is an extremely sensitive and specific marker for DPC4 gene alterations in pancreatic carcinomas. The sensitivity and specificity of immunohistochemical labeling for Dpc4 in other periampullary carcinomas has yet to be determined.

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).

Dpc-4 Protein Is Expressed in Virtually All Human Intraductal Papillary Mucinous Neoplasms of the Pancreas: Comparison with Conventional Ductal Adenocarcinomas

DPC4 (MADH4, SMAD4) encodes a nuclear transcription factor shown to be genetically inactivated in over one-half of conventional infiltrating ductal adenocarcinomas of the pancreas. Intraductal papillary mucinous neoplasms (IPMNs) of the pancreas have been suggested to be distinct neoplasms with a significantly less aggressive course than conventional ductal adenocarcinomas of the pancreas, but molecular comparisons of these tumor types have previously been impaired by technical difficulties. Recently, immunohistochemical labeling for the DPC4 gene product has been shown to be an extremely sensitive and specific marker for DPC4 gene alterations in pancreatic adenocarcinomas. Therefore, we analyzed the immunohistochemical expression of Dpc4 protein in 79 IPMNs using a previously characterized monoclonal antibody. Twenty-nine of the IPMNs also had an associated infiltrating adenocarcinoma available for analysis. The labeling patterns observed were compared to those we have previously reported for conventional ductal carcinomas. All 79 of the intraductal components of the IPMNs strongly expressed Dpc4 protein. In 77 of the 79 cases (97%), the labeling was diffusely positive, and in 2 of the 79 (3%) the labeling was focally positive. Dpc4 expression was seen in 28 (97%) of the associated 29 invasive cancers. The one infiltrating carcinoma that showed loss of Dpc4 expression was associated with an intraductal component which showed focal loss of Dpc4 expression. The strong and almost universal expression of Dpc4 in IPMNs contrasts sharply with the loss of Dpc4 expression seen in approximately 30% of in situ adenocarcinomas of the pancreas (so-called pancreatic intraepithelial neoplasms, grade 3; P: < 0.001) and in 55% of pancreatic duct carcinomas (P: < 0.0001). Differences in Dpc4 expression between IPMNs and ductal carcinomas suggest a fundamental genetic difference in tumorigenesis, which may relate to the significantly better clinical outcomes observed for IPMNs.

MUC4 Expression Increases Progressively in Pancreatic Intraepithelial Neoplasia

Pancreatic adenocarcinoma is believed to develop from histologically identifiable intraductal lesions known as pancreatic intraepithelial neoplasias (PanINs) that undergo a series of architectural, cytologic, and genetic changes, a progression model similar to the adenoma-carcinoma sequence in the colon. The apomucin MUC4 has been implicated in invasive pancreatic adenocarcinoma. MUC4 expression is not detectable at the RNA level in normal pancreas but is detectable at high levels in invasive pancreatic adenocarcinoma. We documented the pattern of expression of MUC4 in PanINs by studying a series of 71 PanIN lesions immunohistochemically using a new monoclonal antibody to MUC4. Five (17%) of 30 PanIN-1 lesions, 10 (36%) of 28 PanIN-2 lesions, 11 (85%) of 13 PanIN-3 lesions, and 25 (89%) of 28 invasive adenocarcinomas labeled with the MUC4 antibody used in the study. In addition, afew nonneoplastic lesions labeled with the MUC4 antibody, including reactive ducts in chronic pancreatitis, atrophic ducts filled with inspissated secretions, and ducts showing squamous metaplasia. Our data help establish the patterns of MUC4 expression in neoplastic precursors in the pancreas and add further support to the progression model for pancreatic adenocarcinoma.

Pathologic examination accurately predicts prognosis in mucinous cystic neoplasms of the pancreas.

The behavior of pancreatic mucinous cystic neoplasms has long been debated. Some authors contend that histologically benign neoplasms can recur and metastasize. We reviewed the gross and microscopic findings and outcomes of 61 mucinous cystic neoplasms diagnosed at The Johns Hopkins Hospital from March 20, 1984 to July 8, 1998. Each neoplasm was placed into one of four categories based on complete histologic examination: invasive mucinous cystadenocarcinoma, mucinous cystic neoplasm with in situ carcinoma, borderline mucinous cystic neoplasm, and mucinous cystadenoma. Neoplasms in the latter three categories were included only if they were entirely resected and completely examined. Patient outcomes were obtained from hospital records and patient and physician follow-up. Twenty (33%) of the patients had invasive mucinous cystadenocarcinomas, and they had 2- and 5-year disease-specific survival rates of 67% and 33% (mean follow-up of survivors, 4.2 years), respectively. Nine (15%) patients had mucinous cystic neoplasms with in situ carcinoma (mean follow-up of survivors, 4.1 years). Five (8.2%) patients had borderline mucinous cystic neoplasms (mean follow-up of survivors, 5.6 years). Twenty-seven (44%) patients had mucinous cystadenomas (mean follow-up of survivors, 5.1 years). No mucinous cystadenoma, borderline mucinous cystic neoplasm, or mucinous cystic neoplasm with in situ carcinoma recurred or metastasized. No patient with the diagnosis of mucinous cystadenoma, borderline mucinous cystic neoplasm, or mucinous cystic neoplasm with in situ carcinoma died of disease. The difference in disease-specific survival rates between patients with invasive mucinous cystadenocarcinomas and those with noninvasive tumors was significant (p < 0.0001, log-rank test). One case, originally showing only benign histology on incisional biopsy, contained foci of invasive carcinoma on complete resection. Completely resected and entirely examined mucinous cystadenomas, borderline mucinous cystic neoplasms, and mucinous cystic neoplasms with in situ carcinoma follow benign courses. Because invasive carcinoma can be focal, failure to study an entire mucinous cystic neoplasm may result in the miscategorization of a malignant neoplasm as benign.

Genetic, immunohistochemical, and clinical features of medullary carcinoma of the pancreas: A newly described and characterized entity.

Medullary carcinomas of the pancreas are a recently described, histologically distinct subset of poorly differentiated adenocarcinomas that may have a unique pathogenesis and clinical course. To further evaluate these neoplasms, we studied genetic, pathological, and clinical features of 13 newly identified medullary carcinomas of the pancreas. Nine (69%) of these had wild-type K-ras genes, and one had microsatellite instability (MSI). This MSI medullary carcinoma, along with three previously reported MSI medullary carcinomas, were examined immunohistochemically for Mlh1 and Msh2 expression, and all four expressed Msh2 but did not express Mlh1. In contrast, all of the medullary carcinomas without MSI expressed both Msh2 and Mlh1. Remarkably, the MSI medullary carcinoma of the pancreas in the present series arose in a patient with a synchronous but histologically distinct cecal carcinoma that also had MSI and did not express Mlh1. The synchronous occurrence of two MSI carcinomas suggests an inherited basis for the development of these carcinomas. Indeed, the medullary phenotype, irrespective of MSI, was highly associated with a family history of cancer in first-degree relatives (P < 0.001). Finally, one medullary carcinoma with lymphoepithelioma-like features contained Epstein-Barr virus-encoded RNA-1 by in situ hybridization. Therefore, because of medullary carcinomas special genetic, immunohistochemical, and clinical features, recognition of the medullary variant of pancreatic adenocarcinoma is important. Only by classifying medullary carcinoma as special subset of adenocarcinoma can we hope to further elucidate its unique pathogenesis.