Morphologic study of three cases of insulinoma. Histochemical and ultrastructural studies.

Ultrastructural and immunocytochemical features of three human insulinomas, one with metastases and the other two with psammoma bodies and amyloid, respectively, are described. Neoplastic cells of all patients reacted with antihuman insulin antibody using the peroxidase-antiperoxidase (PAP) method. Ultrastructurally, neoplastic cells consisted of light cells and dark cells, both of which had a large number of secretory granules, microfilaments, ceroid bodies, and phagolysosomes. Psammoma bodies seemed to originate from neoplastic cell debris in one tumor. In another case, amyloid fibrils appeared to be produced by tumor cells, and there was a close association of amyloid with secretory granules.