Argentaffin carcinoid tumor of the rectum

A case of rectal carcinoid tumor in a 79-year-old Japanese man is reported. The tumor, 1.5 x 0.9 cm, was localized in both mucosa and submucosa of the rectum with neither invasion nor metastasis. Microscopically, neoplastic cells were mainly arranged in rosette-like and trabecular structures within thin fibrous stroma. Histochemically, both argyrophil and argentaffin reactions were positive. At the ultrastructural level, two distinctive types of neurosecretory granules were found in the cytoplasm of tumor cells.