Carcinoid is a relatively benign tumor of the gastrointestinal tract and is thought to originate from the chromaffin cells in the mucosa. Although most commonly located in the appendix, carcinoids have been found from the cardia of the stomach to the rectum. Occasionally these tumors become more malignant and invade adjacent tissues and metastasize to the liver and other distant organs. Histologically no differentiation can be made between the small, apparently benign lesion and the distant metastatic tumors. Thus, many workers feel that all carcinoid lesions are potentially malignant. Although most carcinoids are discovered incidentally at the time of surgery or autopsy, it is now apparent that some carcinoids produce a variety of clinical manifestations through secretion of the pharmacologically active agent, serotonin (5-hydroxytryptamine).
Recently an unusual clinical syndrome has been described which is associated with "malignant" carcinoid of the small intestine and metastasis to the
SJOERDSMA A, TERRY LL, UDENFRIEND S. MALIGNANT CARCINOID a new metabolic disorder. AMA Arch Intern Med. 1957;99(6):1009-1012. doi:10.1001/archinte.1957.00260060167014