Coexpression of insulin and somatostatin in single secretory granules of a pancreatic endocrine tumor.

Pancreatic endocrine tumors, examined by immunohistochemistry, were found to be associated with multihormonal production, and recent studies, performed by employing double immunostaining methods, reported the coexpression of hormones in single cells or in single secretory granules. These findings have been attributed to the heterogeneity of the neoplastic cell population, characterized by the emergence of clones with different phenotypes, and were considered a sign of cell dedifferentiation or malignancy. In this study we describe a case of pancreatic endocrine tumor that showed focal colocalization of insulin and somatostatin in single secretory granules, by means of double labelling immunoelectron microscopy. We think that this observation can be linked to the hypothesis of those authors who speculated upon the appearance of polycrine cells in human fetal pancreas during embryogenesis.