Update on the diagnosis and treatment of rare neuroendocrine tumors

A growing knowledge and awareness of bizarre clinical presentations, the physiology of new peptides, and the more frequent use of radioimmunoassay techniques has led to the identification of more patients with glucagonomas, somatostatinomas, vipomas, and ectopic tumors. Definite clinical syndromes, though sometimes seemingly "silent," occur as a result of hypersecretion of newly identified hormones and neurotransmitters that act in endocrine, neurocrine, or paracrine fashion to alter normal metabolism of carbohydrates and electrolytes. Metabolically and clinically, glucagonomas are catabolic, somatostatinomas are inhibitory, and vipomas are diarrheogenic. The clinical syndromes can be differentiated from other, more common, endocrinopathies; the measurement of the plasma concentrations of the specific peptides is not only diagnostic, but prognostic. Specific pathologic confirmation of the functional potential of these tumors by immunocytochemical techniques is now possible. The goal of diagnosis is detection and tumor localization before metastases occur so that surgical excision may be curative. Objective clinical and humoral responses to chemotherapy for nonresectable or metastatic lesions can be expected in about 50 per cent of patients; specifically, dacarbazine (DTIC) is the agent of choice for glucagonomas, streptozotocin for somatostatinomas, and leukocyte interferon for vipomas.