Somatostatin-producing neuroendocrine tumor of the ampulla (ampullary somatostatinoma). Evidence of prosomatostatin production.

Two cases of somatostatin-producing ampullary neuroendocrine tumors (somatostatinoma) are reported. The authors have characterized their immunoreactivity using antibodies specific for the amino- and carboxyl-terminal portions of prosomatostatin, the precursor of somatostatin in the normal synthetic pathway. Cytoplasmic staining was found using each of these two antibodies in the tumor cells of both ampullary somatostatinomas as well as in the cytoplasm of cells in the hypothalamus, crypt cells of the duodenal mucosa, mucosal cells of the biliary tract, D cells of the pancreatic islets, and parafollicular cells of fetal thyroid. These studies suggest that the synthesis of somatostatin in ampullary somatostatinomas occurs through the normal pathway from the precursor prosomatostatin.