Human pancreatic polypeptide (HPP) immunoreactivity in an infiltrating endocrine tumour of the papilla of Vater with unusual morphology.

Histological, histochemical and clinical features of an endocrine duodenal tumour situated in the papillary region were studied. The tumour had a remarkable mixed histological growth pattern, consisting of epithelial glandular structures which showed a gradual transition into a spindle-cell tumour, resembling a neurogenic tumour. The neoplasm was considered malignant since it had infiltrated into the muscular layer of the duodenal wall. The tumour was non-argentaffin and non-argyrophil. No serotonin could be demonstrated histochemically. Immunoreactive pancreatic polypeptide (HPP) was detected by indirect immunofluorescence in the majority of tumour cells of the epithelial glandular structures, whereas areas with a spindle-cell pattern were almost unreactive to the HPP-antiserum. No reaction was found with antibodies against gastrin, insulin, glucagon, vasoactive intestinal polypeptide or somatostatin. The patient had no endocrine symptoms that could be ascribed to the production of HPP by the neoplasm. Twenty-four months postoperatively, the patient's serum HPP concentration had begun to rise, suggesting recurrence of the tumour.