Electron microscopic and immunoelectron microscopic demonstration of pancreatic polypeptide cells in glucagonoma: colocalization of pancreatic peptide and glucagon in single secretory granules.

We describe a case of pancreatic tumor in a 65-year-old woman with typical glucagonoma syndrome. Plasma glucagon (GL) and pancreatic polypeptide (PP) were markedly elevated up to 1404 and 1200 pg/ml, respectively. Histologic examination of the metastatic tumors in liver and lymph nodes showed endocrine-type tumors composed of GL-positive cells some of which coexpressed PP immunoreactivity. Electron microscopy revealed the tumor cells with single-type secretory granules similar to normal A cell granules. Double immunogold staining demonstrated both GL and PP immunoreactivities in the same secretory granules. Biologic and diagnostic significance of coexpression of PP and GL in a single secretory granules of pancreatic endocrine tumors is discussed briefly.