Carcinoid is the term currently used to describe the major tumor of the neuroendocrine tumor family. The term “carcinoid” was first used about a century ago. It was applied by a German pathologist Otto Lubarsch in 1888 to a group of tumors which he studied and which develop in the intestine. They are visually quite different but functionally similar in their properties to ordinary carcinomas. In addition, the carcinoid tumors are not quite benign. Therefore he coined the term “carcinoid” as describing an intermediate type of malignancy, that grows more slowly than the more common intestinal carcinoma and which does not have the classical functional appearance of a carcinoma. Today, the term carcinoid is employed to describe a group of intestinal carcinoid tumors that are derived from enterochromaffin cells (ECL), which are cytochemically indistinguishable from many of the gastrointestinal hormone-secreting cells of the intestinal tract. The most frequent sites of their location are the ileum and the appendix. The chief clinical signs of carcinoid syndrome are extensive body flushing notable on the face and arms and also diarrhea.
Carcinoid tumors are now known to be found most commonly in the GI tract and lungs. Some rare examples of carcinoid sites include the heart, testes, and ovaries, and they have the ability to metastasize to the liver. Carcinoid tumors normally range from 1–2 cm in diameter. The clinical “label” of carcinoid syndrome was introduced in 1954.
The chief biochemical lesion is an elevated production of 5-hydroxytryptamine, which results from the conversion of tryptophan to 5-hydroxytryptophan followed by decarboxylation to yield 5-hydroxytryptamine. Elevated blood levels of 5-hydroxytryptamine and an increased urinary excretion of 5-hydroxyindole-acetic acid are often diagnostic of the carcinoid syndrome. Also, the tumor contains the enzyme kallikrein, which leads to increased plasma levels of bradykinin.
Originally carcinoid was an extremely rare tumor; however, in the last 15 years it has been diagnosed with greater frequency. Presently, there are about 3,000 4,000 new carcinoid cases appearing and being reported in the United States every year. There are now ~50,000 subjects with carcinoid of clinically significant degree. Of course, this rate of frequency is still rather uncommon when viewed from the perspective of the more frequently encountered growths like cancer of the breast (230,000 per year) or prostate (240,000/year), both in 2012. Both pharmacological and surgical treatments are employed to treat carcinoid syndrome.
