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Clinical features of the carcinoid syndrome

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


Carcinoid syndrome is the term applied to a constellation of symptoms mediated by various humoral factors elaborated by some carcinoid tumors (ie, neuroendocrine tumors of the digestive tract and lungs). These tumors synthesize, store, and release a variety of polypeptides, biogenic amines, and prostaglandins (table 1). Some of these tumor products are responsible for the carcinoid syndrome, but the relative contributions of each and the specificity of any for particular components of the syndrome are uncertain (table 2).

Carcinoid tumors may arise anywhere in the gastrointestinal tract, in the bronchi, and occasionally, elsewhere (table 3). The liver inactivates bioactive products secreted into the portal circulation. This may explain why patients with gastrointestinal carcinoid tumors typically develop the carcinoid syndrome if they have hepatic metastases, resulting in the secretion of tumor products into the systemic circulation [1]. In the large majority of cases, the carcinoid syndrome is associated with metastatic tumors originating in the midgut (jejunum, ileum, and cecum). Bronchial carcinoid tumors are associated with the carcinoid syndrome in approximately 10 percent of cases. Hindgut tumors (distal colon and rectum) are hormonally silent in nearly all cases. Approximately 1 percent of pancreatic neuroendocrine tumors secrete excess serotonin and other vasoactive substances that produce the carcinoid syndrome. (See "Clinical characteristics of carcinoid tumors".)

The pathophysiology and clinical manifestations of the carcinoid syndrome will be reviewed here. The diagnosis and treatment of this disorder are discussed separately. (See "Diagnosis of the carcinoid syndrome and tumor localization" and "Staging, treatment, and posttreatment surveillance of nonmetastatic, well-differentiated gastrointestinal tract neuroendocrine (carcinoid) tumors" and "Metastatic well-differentiated gastroenteropancreatic neuroendocrine tumors: Presentation, prognosis, imaging, and biochemical monitoring".)


As many as 40 secretory products have been identified in various carcinoid tumors [1]. The most prominent of these are serotonin, histamine, tachykinins, kallikrein, and prostaglandins (table 1).

Tryptophan metabolism — Altered metabolism of tryptophan occurs in almost all patients with the carcinoid syndrome. In normal subjects, approximately 1 percent of dietary tryptophan is converted to serotonin; however, this value may increase to 70 percent or more in patients with the carcinoid syndrome [2]. Serotonin is then metabolized to 5-hydroxyindoleacetic acid (5-HIAA) (figure 1).


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Literature review current through: Apr 2017. | This topic last updated: Mar 30, 2017.
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