Case 3 -

Precursor Lesions of the Duodenum and Pancreas (No slides submitted) Martin Anlauf, Department of Pathology, University of Kiel , Germany Aurel Perren, Department of Pathology, University Hospital Zürich , Switzerland Tobias. Henopp, Department of Pathology, University of Kiel , Germany Regina Schlenger, Department of Pathology, University of Kiel , Germany Nele . Garbrecht, Department of Pathology, University of Kiel , Germany Marie L. Kruse, 1st Department of Medicine, Laboratory for Molecular Gastroenterology and Hepatology, University of Kiel , Germany Eberhard WeiheDepartment of Molecular Neuroscience, Institute of Anatomy and Cell Biology, Philipps University , Marburg , Germany O. Gimm, Department of General and Visceral Surgery, University of Halle , Germany H. Dralle, Department of General and Visceral Surgery, University of Halle , Germany Andreas Raffel, Department of General and Visceral Surgery, University of Halle , Germany Wolfram T. Knoefel, Department of General and Visceral Surgery, University of Halle , Germany Paul Komminoth, Department of Pathology, University Hospital Zürich and Kantonsspital Baden, Switzerland Philipp U. Heitz, Kantonsspital Baden, Baden, Switzerland Günter Klöppel, Department of Pathology, University of Kiel , Germany (Martin Anlauf and Aurel Perren both contributed equally)

General remarks For diagnosis and therapy as well as for the understanding of the tumorigenesis of malignant tumors it is particularly important to identify precursor lesions that represent a sequence of cellular changes from hyperplasia to neoplasia. There are several endocrine tumors that develop on the basis of hyperplastic changes, i.e. medullary thyroid carcinoma or pheochromocytoma. Furthermore, it is likely that the adenomatous changes of the parathyroid in multiple endocrine neoplasia type 1 (MEN1) patients originate from hyperplastic changes .All such conditions, except for the ECL-cell hyperplasia in chronic atrophic gastritis, are associated with an inherited endocrine disorder. This lecture focuses on the morphological aspects of precursor lesions of sporadic and hereditary duodenal and pancreatic neuroendocrine tumors (NETs) with special emphasis on MEN1-associated tumors. Molecular concepts of tumor development and clinical implications are discussed. Duodenal NETs The most common neuroendocrine tumor type of the duodenum is gastrin-producing tumors. [1, 2] Most of them are associated with a Zollinger–Ellison syndrome (ZES) due to inappropriate gastrin secretion. ZES is characterized by elevated fasting gastrin serum levels, a positive gastrin secretin stimulation test and clinical symptoms such as recurrent peptic ulcer disease, gastroesophageal reflux disease and occasional diarrhea. [3, 4] Though duodenal gastrinomas are often of small size (diameter less than 1 cm) they tend to metastasize early to regional lymph nodes and the liver. Clinically, sporadic and hereditary gastrinomas behave differently. While 30-40% of sporadic gastrinomas can be cured by local excision and lymphadenctomy, in patients with MEN1-associated duodenal gastrinomas the ZES persists. [4] In 1990 it was noticed that many duodenal gastrinomas arising in the setting of MEN1 are multiple, in contrast to sporadic gastrinomas. [5] Recently, it has been shown that multicentric duodenal gastrinomas are associated with a wide range of gastrin cell precursor lesions within the nontumorous duodenal mucosa. [6] These included diffuse, linear and micronodular changes of gastrin cells as well as gastrin-producing microtumors with a diameter of 300 μm in size. In 12 MEN1 patients 26 of these gastrin-positive microtumors with a mean diameter of 0.6 mm (0.3-1.8 mm) were detected. Each of these patients exhibited linear, diffuse and nodular gastrin cell changes. Simple, linear and micronodular gastrin cell hyperplasia was far more common than enlarged nodules and early invasive lesions. The proliferative nature of these lesions was confirmed by expression of the Ki-67 antigen, while expression of Ki-67 was absent from nonhyperplastic gastrin cells. The MEN1 germline mutations were associated with the phenotype of gastrin cell hyperplasia, multifocal gastrinomas and the presence of MEN1 associated extraduodenal NETs. In contrast, all patients who lacked gastrin cell hyperplasia, multifocal gastrinomas and/or MEN1-associated extraduodenal NETs also did not show any mutations. In summary, duodenal gastrinomas in MEN1 but not sporadic gastrinomas are associated with a wide range of gastrin cell lesions in the nontumorous mucosa, suggesting that gastrinomas in patients with the MEN1 syndrome evolve from these lesions. The identification of preneoplastic gastrin cell lesions in biopsy specimens from the duodenum may be of diagnostic relevance and may influence the clinical management of these patients. Pancreatic NETs Most pancreatic NETs are sporadic tumors. Approximately 10% of pancreatic NETs arise on the hereditary background of MEN1. [3, 7, 8] The presence of multiple small endocrine tumors in the pancreas (i.e. up to 5 mm in diameter) has been referred to as microadenomatosis and has been observed in association with the MEN1 syndrome. In MEN1, pancreatic microadenomatosis is usually accompanied by one or more macrotumors (diameter >5 mm), some of which may be functionally active. [3, 8] Although the identification of the MEN1 gene on 11q13 has led to extensive studies of the genetic and clinical features of the MEN1 syndrome, our knowledge of the development and pathology of pancreatic endocrine neoplasms in MEN1 is mainly based on reports of single cases. Only few studies on a series of MEN1 patients have been published. [9, 10, 11, 12] They showed that microadenomatosis in MEN1 patients is highly variable as far as the number of tumors and their hormonal profiles are concerned. Although these microadenomas express pancreatic hormones such as insulin and glucagon, they are thought to be nonsymptomatic. Genetically, they show a loss of heterozygosity of the MEN1 gene locus at very early stages of their development. [12] Opinions vary as to which type of endocrine cell lesion precedes the development of pancreatic endocrine tumors in MEN1. On the basis of morphology, it has been suggested that islet cell hyperplasia is a forerunner of pancreatic endocrine tumors in MEN1, but this has been discussed controversially. In a recent study by our group we correlated endocrine microadenomatosis of the pancreas with clinical features and genetic changes that characterize the MEN1 or VHL syndrome. [11] We studied pancreatic specimens surgically removed from 37 patients in whom pancreatic endocrine tumors were suspected and who often had the clinical features of the MEN1 syndrome. In particular, we were interested in answering the following questions: (1) Is pancreatic microadenomatosis a feature of MEN1? (2) Is there a type of microadenomatosis that occurs independently of inherited conditions such as MEN1 or VHL? (3) Can microadenomatosis cause the clinical symptoms of inappropriate hormone secretion? (4) What phenotypic changes in endocrine cells precede tumor development in association with microadenomatosis? Pancreatic microadenomatosis was found in 35 of 37 patients, 28 of whom fulfilled the clinicopathological criteria and 13 the genetic criteria for MEN1, while none of the patients had evidence of a VHL syndrome. Microadenomas were present in 26 of the 28 MEN1 patients. Three hundred twenty-one of the 347 microadenomas (92.5%) expressed islet hormones. Most common was glucagon (181; 52.1%), followed by PP (70; 20.1%), insulin (52; 14.9%) and somatostatin (18; 5.2%). The hormone-positive microadenomas were usually multihormonal with one predominant hormone. All 9 patients without the MEN1 or VHL syndrome had multiple microadenomas. Five of these 9 patients suffered from hyperinsulinemic hypoglycemia and had a total of 9 insulin-positive macrotumors and 42 insulin-positive microadenomas. Two of the 5 patients with hyperinsulinemic hypoglycemia had only insulin-positive microadenomas, most of which were less than 1 mm in diameter. Four further patients had multiple trabecular glucagon-expressing neoplasms, with a total of 10 macrotumors and 817 microadenomas. One patient had more than 600 glucagon-positive microadenomas. Immunohistochemical analysis and confocal laser scanning double fluorescence microscopy of the normal appearing endocrine tissue revealed the following abnormalities, which were not seen in the control pancreatic specimens. (1) linear and nodular hyperplasia of duct-associated endocrine cells and (2) islets that were enlarged or irregularly shaped with an increased ratio of glucagon/insulin cells. In conclusion, we can confirm that pancreatic microadenomatosis is a characteristic hallmark of MEN1. Twenty-eight patients in our study fulfilled the WHO criteria for an MEN1 syndrome, i.e. pancreatic endocrine tumors associated with MEN1-related extrapancreatic endocrine tumors. All but two MEN1 patients revealed pancreatic microadenomatosis. From this detailed analysis we conclude that MEN1 patients have a high probability of developing microadenomatosis of the endocrine pancreas. The absence of microadenomatosis in two patients indicates either that the penetrance of microadenomatosis in MEN1 is not 100% or that there were too few microadenomas to be detected by our sampling method. However, microadenomatosis of the pancreas is not restricted to genetic syndromes such as MEN1 or VHL. A monohormonal type of pancreatic microadenomatosis was identified that consisted of either insulinomas or glucagon-producing tumors and was not associated with MEN1 or VHL. The fact that non-MEN1 patients were clearly separated into two groups with either insulin- or glucagon-producing tumors suggests that they could belong to two disease entities rather than to a single one. Concerning the starting points of neoplastic endocrine cell growth we believe that both compartments, i.e. the duct system and the islets, may harbor preneoplastic progenitor cells that may give rise to microadenomas in MEN1 and non-MEN1 patients. Reference list Capella C, Riva C, Rindi G, et al. Histopathology, hormone products, and clinicopathological profile of endocrine tumors of the upper small intestine: a study of 44 cases. Endocr Pathol 1991;2:92-110. Burke AP, Federspiel BH, Sobin LH, et al. Carcinoids of the duodenum. A histologic and immunohistochemical study of 65 tumors. Am J Surg Pathol 1989;13:828-837. Marx SJ, Simonds WF. Hereditary hormone excess: genes, molecular pathways, and syndroms. Endocrine Reviews 2005;615-661. Norton JA, Fraker DL, Alexander HR, et al. 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