ABSTRACT
Neuroendocrine tumors (NETs) are found throughout the intestinal tract and arise from
the Kulchitsky cells located in the crypts of Lieberkühn. They are classified by site
of origin and by degree of differentiation, with well-differentiated lesions representing
those tumors formerly referred to as carcinoid tumors. The focus of this review is
NETs of the appendix, colon, and rectum. The clinical presentation of these tumors
is dependent on the primary site and many are discovered incidentally, either during
screening or during the investigation of nonspecific abdominal complaints. Treatment
is primarily via surgical removal as the response to chemotherapy has been traditionally
poor. A noted exception to this has been with treatment of the carcinoid syndrome,
which occurs almost exclusively in patients with liver metastases and is due to the
release of bioactive peptides and amines directly into the systemic circulation. The
use of somatostatin congeners to block the release of these substances has greatly
ameliorated the devastating symptoms of this condition. Postresection follow-up is
advocated, but specific recommendations are lacking an evidentiary basis. NETS, particularly
those of the small bowel, colon, and appendix, are seen in association with other
synchronous or metachronous malignancies, often of the gastrointestinal tract. However,
the utility of subsequent screening and surveillance is unproven.
KEYWORDS
NETs - carcinoid tumor - carcinoid syndrome - serotonin - somatostatin
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John Carl EggenbergerM.D.
Associates in General and Vascular Surgery, Michigan Heart and Vascular Institute
5325 Elliott Dr., Ste. 104, Ypsilanti, MI 48197
eMail: eggenbej@trinity-health.org