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Overview of Carcinoid Tumors

By B. Mark Evers, MD, Professor and Vice-Chair of Surgery; Markey Cancer Foundation Endowed Chair; Director, Lucille P. Markey Cancer Center; Physician-in-Chief, Oncology Service Line UK Healthcare, University of Kentucky

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Carcinoid tumors develop from neuroendocrine cells in the GI tract (90%), pancreas, and pulmonary bronchi. More than 95% of all GI carcinoids originate in only 3 sites: the appendix, ileum, and rectum.

Although carcinoids are often benign or only locally invasive, those affecting the ileum and bronchus are frequently malignant.

Carcinoids can be

  • Endocrinologically inert

  • Endocrinologically active (produce hormones)

The most common endocrinologic syndrome is carcinoid syndrome; however, most patients with carcinoid tumors do not develop carcinoid syndrome. The likelihood that a tumor will be endocrinologically active varies with its site of origin, being highest for tumors originating in the ileum and proximal colon (40 to 50%). The likelihood is lower with bronchial carcinoids, lower still with appendiceal carcinoids, and essentially zero with rectal carcinoids.

Endocrinologically inert carcinoids are suspected because of their symptoms and signs (eg, pain, luminal bleeding, GI obstruction). They can be detected by angiography, CT, or MRI. Small-bowel carcinoids may exhibit filling defects or other abnormalities on barium x-rays. Definitive diagnosis is made histologically after biopsy or resection.

Treament of nonmetastatic carcinoid tumors is usually surgical resection. The type of surgery depends on the location in the GI tract and the size of the tumor.

Endocrinologically active carcinoids are diagnosed and treated as described for carcinoid syndrome.