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Clinical characteristics of well-differentiated neuroendocrine (carcinoid) tumors arising in the tubular digestive tract, lung, and genitourinary tract

Jonathan R Strosberg, MD
Section Editors
Kenneth K Tanabe, MD
David C Whitcomb, MD, PhD
Deputy Editor
Diane MF Savarese, MD


The term "carcinoid" is generally applied to well-differentiated neuroendocrine tumors (NETs) originating in the tubular digestive tract, lungs, or rare primary sites, such as the kidneys or ovaries. Use of the term carcinoid implies well-differentiated (low- to intermediate-grade) histology and is not traditionally used to describe high-grade poorly differentiated NETs, which are now classified as neuroendocrine carcinomas. Well-differentiated NETs that arise in the pancreas, while histologically similar to those arising in the tubular portion of the gastrointestinal tract, are not referred to as "carcinoids" but instead as pancreatic NETs (table 1). (See "Pathology, classification, and grading of neuroendocrine tumors arising in the digestive system", section on 'Pathology, tumor classification, and nomenclature'.)

"Carcinoid syndrome" is the term applied to a constellation of symptoms mediated by various humoral factors that are elaborated by some well-differentiated NETs arising in the gastrointestinal tract (GINETs) (table 2) [1]. Typical carcinoid syndrome, consisting primarily of flushing and diarrhea (table 3), occurs predominantly in patients with metastatic NETs originating in the small intestine. Carcinoid syndrome is rare with lung or genitourinary well-differentiated NETs. (See "Clinical features of the carcinoid syndrome".)

Well-differentiated NETs are rare overall, but their age-adjusted incidence in the United States has increased significantly, partly due to increased detection on radiographic imaging and endoscopy.

This topic will cover the epidemiology, classification, and clinical features of primary well-differentiated NETs (carcinoid tumors) arising in the gastrointestinal and genitourinary systems. The pathology and nomenclature of digestive tract NETs; clinical features and diagnosis of carcinoid syndrome; issues related to tumor localization in well-differentiated GINETs; features and management of high-grade gastroenteropancreatic neuroendocrine carcinoma, bronchial NETs, and thymic NETs; and the management of patients with nonmetastatic and metastatic well-differentiated GINETs are discussed separately.

(See "Pathology, classification, and grading of neuroendocrine tumors arising in the digestive system".)

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Literature review current through: Dec 2017. | This topic last updated: Oct 20, 2017.
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