Histogenesis of a duodenal carcinoid

A duodenal carcinoid with a diameter of 9 mm was cut serially into 5 microns thin sections from one end to the other. Every fourth section was stained with the argyrophil method of Grimelius, while representative sections in between were used for immunohistochemical analyses. The tumor displayed an argyrophil reaction and was chromogranin A immunoreactive and S-100 protein negative. Furthermore, the majority cell population was gastrin-immunoreactive, while minor cell populations stained for somatostatin and serotonin. The serial sectioning revealed that the tumor arose from differentiated endocrine cells located in the mucosal crypts. In the duodenal mucosa in the vicinity of the tumor the epithelial crypts exhibited an increased number of endocrine cells, preferentially displaying gastrin immunoreactivity. The results indicate that in this particular case the carcinoid tumor arose from hyperplastic and differentiated endocrine cells in the epithelial crypts of the duodenal mucosa.