How are carcinoid tumors classified?

Updated: Feb 12, 2019
  • Author: Cameron K Tebbi, MD; Chief Editor: Max J Coppes, MD, PhD, MBA  more...
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Carcinoid tumors generally are classified based on the location in the primitive gut (ie, foregut, midgut, hindgut) that gives rise to the tumor.

Foregut carcinoid tumors are divided into sporadic primary tumors and tumors secondary to achlorhydria. The term sporadic primary foregut tumor encompasses carcinoids of the lung, bronchus, stomach, proximal duodenum, and pancreas.

Midgut tumors are derived from the second portion of the duodenum, the jejunum, the ileum, and the right colon. The image below shows the distribution of carcinoid tumors.

Distribution of carcinoid tumors. Distribution of carcinoid tumors.

These account for 60-80% of all carcinoid tumors (especially those of the appendix and distal ileum) in adults and are also seen in children. [29] Appendicular carcinoid tumors are most common. [30, 31] In children, more than 70% of these tumors occur at the tip of the appendix and are often an incidental finding in appendectomy specimens. In one study, carcinoid tumors were found in 0.169% of 4747 appendectomies. [32] Bulky tumors are relatively rare and require somewhat extensive cecectomy or, when tumor infiltration is beyond the cecum, ileocecal resection. [34, 35, 31]

Hindgut carcinoid tumors include those of the transverse colon, descending colon, and rectum.

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