CYTOKERATIN EXPRESSION IN SMALL-INTESTINAL AND APPENDICEAL CARCINOIDS- A BASIS FOR CLASSIFICATION

For a study of histogenesis of intestinal carcinoids a collection of 5 classical small intestinal carcinoids, 6 appendiceal carcinoids and 9 pheochromocytomas, were evaluated. The tumors were identified by rout ine morphology, silver staining and chromogranin immunocytochemistry a nd were then examined with regard to the expression of intermediate fi laments of cytokeratin type. Eight different antisera identifying indi vidual or combinations of cytokeratins were employed. All classical sm all intestinal carcinoids displayed cytokeratin immunoreactivity and a n almost identical cytokeratin reaction was observed in the normal ent erocytes of the small intestinal mucosa. Of the individual cytokeratin types, number 18 was most heavily expressed. The appendiceal carcinoi ds, like the pheochromocytomas, almost totally lacked a cytokeratin st aining despite a positive reaction in the mucosa of the appendix. This , in agreement with some previous studies, indicates that the small in testinal carcinoids are histogenetically related to the epithelial cel ls of the intestinal mucosa, while the appendiceal carcinoids have a d ifferent histogenesis and are more like pheochromocytomas. The appendi ceal carcinoid may represent a distinct type of intestinal paraganglio ma. This offers one explanation for the different biological behavior of appendiceal carcinoids in comparison with the other intestinal carc inoids.