Are pancreatic VIPomas paraneuron neoplasms? A clue to the neuroectodermal origin of these tumors.

Three pancreatic vasoactive intestinal polypeptide (VIP)-producing tumors associated with the watery diarrhea-hypokalemia-achlorhydria syndrome were studied histologically, ultrastructurally, and immunocytochemically. All the tumors contained varying numbers of cells arranged in pseudoglandular structures. The cells showed a polar organization, with apical tuft of microvilli and basal VIP-containing, synaptic vesicle-like granules. Based on the morphology of the VIPoma cells typical of recepto-secretory cells, together with the ability to synthesize and release a peptide that in normal conditions is expressed exclusively by neurons, and the absence of VIP-producing endocrine cells in normal pancreas and gastrointestinal mucosa, the hypothesis is drawn that the pancreatic VIPomas reported here are paraneuron neoplasms, which possibly originate from neuroectodermal ancestors.