Pancreatic polypeptide-secreting islet-cell tumors. A study of three cases

Three cases of pancreatic islet cell tumors, 1 malignant and 2 benign, producing predominantly pancreatic polypeptide (PP) are described. All 3 patients exhibited elevated plasma PP concentrations, either basal or protein-meal-stimulated, during the period of observation. Immunocytochemical study revealed that while PP cells predominated in the tumor, A, B, and D cells were also present. A comparison of the hormone content of the tumor tissue, adjacent pancreatic tissue, and normal pancreas was made by radioimmunoassay of tissue extracts. The PP content of tumors clearly exceeded that of normal pancreas. The insulin, glucagon, and somatostatin (SRIF) content was more variable, but in one case the glucagon content of the tumor was higher than in normal pancreas, and two of the tumors exhibited an elevated SRIF content. Gel filtration of a tumor extract showed that insulin, glucagon, and PP immunoreactivity was of expected molecular dimensions but immunoreactive SRIF in this extract was composed of two species. The PP in gel fractions reacted equally well with antibody directed toward different parts of the PP molecule.