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Diagnosis of the carcinoid syndrome and tumor localization

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


The term "carcinoid" has been generally applied to well-differentiated neuroendocrine tumors (NETs) originating in the digestive tract, lungs, or rare primary sites, such as the kidneys or ovaries. In modern usage, the term carcinoid is still used to refer to well-differentiated NETs arising in the lung (typical or atypical carcinoids), but within the gastrointestinal tract, the term carcinoid has fallen out of favor, and the World Health Organization preference is for the term NET. Regardless of site, the term "neuroendocrine carcinoma" is usually assigned to high-grade or poorly differentiated NETs. (See "Pathology, classification, and grading of neuroendocrine tumors arising in the digestive system", section on 'Pathology, tumor classification, and nomenclature'.)

NETs can present in several different ways:

As a result of the carcinoid syndrome: Chronic flushing and/or diarrhea are the typical manifestations of the carcinoid syndrome, which is the result of secretion of serotonin and other vasoactive substances into the systemic circulation. The carcinoid syndrome is primarily associated with metastatic tumors originating in the midgut (distal small intestine and proximal colon). In contrast, hindgut (distal colorectal) and foregut (gastroduodenal, lung) NETs uncommonly produce the carcinoid syndrome. (See "Clinical features of the carcinoid syndrome" and "Lung neuroendocrine (carcinoid) tumors: Epidemiology, risk factors, classification, histology, diagnosis, and staging", section on 'Presenting signs and symptoms'.)

As a result of tumor growth: Small bowel NETs may cause chronic/recurrent abdominal pain, occasionally leading to bowel obstruction. Metastatic tumors in the liver can cause right upper quadrant pain, hepatomegaly, and early satiety. (See "Clinical characteristics of carcinoid tumors", section on 'Jejunoileal small bowel tumors' and "Metastatic well-differentiated gastroenteropancreatic neuroendocrine tumors: Presentation, prognosis, imaging, and biochemical monitoring", section on 'Clinical presentation'.)

As an incidental finding: Many NETs are discovered during endoscopic or radiographic procedures planned for other purposes; this is especially true of carcinoids of the stomach and rectum.

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Literature review current through: Nov 2017. | This topic last updated: May 09, 2017.
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