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| AuthorsJennifer Ang Chan, MD, MPHMatthew Kulke, MD | Section EditorRichard M Goldberg, MD | Deputy EditorDiane MF Savarese, MD |
Topic Outline
INTRODUCTION
Neuroendocrine cells are distributed widely throughout the body, and neoplasms of these dispersed cells can arise at many sites.
Classification and nomenclature — Neuroendocrine tumors (NETs) arising at different sites within the body are classified according to their histologic features. While there are differences in terminology and grading for these tumors arising at different sites, all commonly used classification systems reflect a basic separation between more indolent, well differentiated tumors (which in the digestive system have been traditionally referred to as carcinoids and pancreatic neuroendocrine [islet cell] tumors) and far more aggressive poorly differentiated types that behave clinically more like small cell carcinoma of the lung. (See "Metastatic gastroenteropancreatic neuroendocrine tumors: Presentation, prognosis, imaging, and biochemical monitoring", section on 'Classification and nomenclature'.)
Poorly differentiated neuroendocrine carcinomas are often associated with a rapid clinical course, while well-differentiated NETs generally have a much better prognosis. However, there is a spectrum of aggressiveness for well-differentiated tumors. Even in the presence of liver metastases, some patients may survive for many years. Proliferative rate, as assessed by mitotic count and/or Ki67 labeling index, is of prognostic significance, independent of tumor stage. The World Health Organization (WHO) classifies well-differentiated gastroenteropancreatic NETs into low-grade (G1) and intermediate grade (G2) categories based upon proliferative rate (table 1) [1]. All poorly differentiated neuroendocrine tumors are high-grade (G3) neuroendocrine carcinomas. (See "Pathology, classification, and grading of neuroendocrine tumors arising in the digestive system", section on '2010 WHO classification'.)
This topic review will cover local treatment options for patients with well-differentiated metastatic gastroenteropancreatic NETs. Systemic treatment options to control tumor growth and/or symptoms of hormone hypersecretion and for treatment for poorly differentiated gastroenteropancreatic NETs are discussed elsewhere, as are the clinical presentation, imaging, and biochemical monitoring for patients with advanced gastroenteropancreatic NETs; pathology and classification of gastroenteropancreatic NETs; clinical features of primary carcinoid tumors; diagnosis of carcinoid syndrome and tumor localization; the treatment of early stage carcinoids; bronchial carcinoids; localization and treatment of pancreatic islet cell tumors; evaluation and management of neuroendocrine tumors of unknown primary site; management of symptoms of the carcinoid syndrome; carcinoid heart disease; and functioning pancreatic islet cell tumors.
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