Clinical features of the carcinoid syndrome
- Jonathan R Strosberg, MD
Jonathan R Strosberg, MD
- Associate Professor
- Department of Gastrointestinal Oncology
- H. Lee Moffitt Cancer Center
- Section Editors
- Kenneth K Tanabe, MD
Kenneth K Tanabe, MD
- Section Editor — Gastrointestinal Malignancies
- Professor of Surgery
- Harvard Medical School
- David C Whitcomb, MD, PhD
David C Whitcomb, MD, PhD
- Section Editor — Pancreatic Diseases
- Professor of Medicine
- University of Pittsburgh School of Medicine
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 . 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".)
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 . Serotonin is then metabolized to 5-hydroxyindoleacetic acid (5-HIAA) (figure 1).
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- Tryptophan metabolism
- CLINICAL FEATURES
- Cutaneous flushing
- Venous telangiectasia
- Cardiac valvular lesions
- Minor manifestations
- VARIANT SYNDROMES
- Gastric carcinoid variant syndrome
- Bronchial carcinoid variant syndrome