Human islet cell tumor storing pancreatic polypeptide: a light and electron microscopic study.

A 45-year-old man was operated for surgical treatment of a long-standing peptic ulcer disease and upon inspection of the pancreas for suspected Zollinger-Ellison syndrome, tumor nodules were found in this organ. The tumor tissue examined by immunofluorescence showed specific staining only after incubation with anti-pancreatic polypeptide. Negative results were obtained with antisera directed against insulin, pancreatic glucagon, somatostatin, GLI, VIP, secretin, and gastrin. Examination of the tissue by electron microscopy revealed a homogeneous population of small granule-containing cells. This case, therefore, illustrates a tumor composed of one single hormone-producing cell type and allows definition of the ultrastructural features of human pancreatic polypeptide-containing cells.