Carcinoid tumors have long been anatomical and biochemical curiosities to investigators. There is disagreement as to the character of the tumors, and continued speculation on the exact mechanism by which symptoms are produced. However, it is known now that carcinoid tumors are potentially malignant—capable of local invasion and distant spread.
Grossly, carcinoid tumors appear as small, round to plaque-like, submucosal elevations which are deceptively mobile. The overlying mucosa is usually intact. When sectioned the tissue is yellow. Microscopically, there is no variation in the size and shape of individual cells, with polygonal to cuboidal cells looking much alike. Rarely carcinoid tumors may ulcerate, bleed, or obstruct. Mitosis and anaplasia are rare. For this reason, the usual criteria for judging the malignant potential of a carcinoid tumor are different from those in carcinoma. Gross and microscopic invasion determine the malignancy of a carcinoid tumor. MacDonald1 has stated that a carcinoid tumor that has infiltrated the muscularis of the bowel wall is already in the first stage of malignancy. He has shown that carcinoids metastasize via the blood vessels to lymph nodes, liver, and other distant organs. Although he considered appendiceal carcinoids nonmetastasizing and, therefore, different from carcinoid tumors in other sites, there is evidence to the contrary.2
In 1906 Ciaccio3 suggested that carcinoid tumors had a biochemical activity, i.e., production of epinephrine; but it was not until 1948 that Rapport et al4 crystallized a vasoconstrictor substance from serum extracts and called it serotonin. The following year, the same group5 identified. . .