A malignant tumor of the pancreas producing glucagonoma syndrome: coexistence of glucagon and pancreatic polypeptide (PP) in the tumor cells.

A malignant tumor of the pancreas producing the glucagonoma syndrome and associated with high plasma levels of glucagon and pancreatic polypeptide was studied histologically, ultrastructurally, and immunocytochemically. The histologic and ultrastructural features were closely similar to those of previously reported malignant glucagonomas. However, immunolabeling with specific antisera revealed that, in addition to cells having only glucagon- or only pancreatic polypeptide-immunoreactivity, other cells were also present, showing a co-existence of both peptides. These findings indicate that the tumor contains a cell population with a phenotype similar to that of intestinal L-cells rather than to pancreatic A-cells.