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INTRODUCTION

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Pancreatic neuroendocrine tumors (PNETs) are tumors that originate from the islet cells of the pancreas and are also often referred to as islet cell tumors. With an estimated incidence of about 2.5 to 5 per 100,000 persons per year, these uncommon tumors represent only 1% to 2% of pancreatic malignancies.1 In contrast to pancreatic adenocarcinoma, the incidence of PNETs appears to have increased over the past decades.2,3 Autopsy studies have shown that small, asymptomatic PNETs may occur in as many as 10% of people.4,5 Thus, increased detection, particularly because of increased imaging and advances in imaging technology, may account for much of the rise in the incidence of PNETs.6-8

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In addition to being uncommon, PNETs are also notably heterogeneous with regard to their clinical presentation. PNETs may be classified in several distinct ways: (1) the aggressiveness of malignancy (benign behavior to highly aggressive); (2) the functional status (hormone-producing or not); or (3) the clinical context in which the tumor arises (sporadic or in the context of an inherited syndrome). The overall rarity of PNETs and the heterogeneity of their clinical presentation create challenges in their management. The purpose of this chapter is to present the natural history and basic principles of management of PNETs in their varied forms of presentation.

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GENERAL FEATURES AND CLASSIFICATION OF PANCREATIC NEUROENDOCRINE TUMORS

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Pathologic Features

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Pancreatic neuroendocrine tumors arise from neuroendocrine cells that are scattered diffusely throughout the pancreas. Their malignant potential varies widely from benign to highly aggressive. From a pathologic perspective, PNETs are classified into four general categories: (1) endocrine microadenomas, (2) well-differentiated neuroendocrine carcinomas, (3) poorly differentiated neuroendocrine carcinomas, and (4) mixed endocrine carcinomas (Table 145-1). Ultimately, the only reliable way of determining malignancy is by identifying local invasion, involved regional lymph nodes, or distant metastatic sites.9

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Table Graphic Jump Location
TABLE 145-1

Pathologic Classification of Pancreatic Neuroendocrine Tumors

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ENDOCRINE MICROADENOMAS AND WELL-DIFFERENTIATED NEUROENDOCRINE CARCINOMAS
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The vast majority of PNETs are well-differentiated; that is, they retain normal architecture and have a low proliferative rate. ...

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