LOCATION OF A VIPOMA BY IODINE-123-VASOACTIVE INTESTINAL PEPTIDE SCINTIGRAPHY

A major problem in patients with small endocrine tumors is the difficu lty in localizing the primary tumor site, Many endocrine tumors posses s larger amounts of high affinity vasoactive intestinal peptide (VIP) binding sites compared with normal tissue or blood cells. We used radi olabeled VIP to localize the tumor site in a patient with Verner-Morri son syndrome (VMS), Under octreotide therapy, the VIP levers had decli ned in this patient, but a tumor site could not be detected by convent ional techniques or by radiolabeled octreotide. However, using I-123-V IP, the tumor was detectable in the pancreatic tail. Surgical resectio n of the tumor was followed by complete remission of the VMS. Expressi on of VIP binding sites in the tumor was confirmed by a radioreceptor assay and showed cross-competition between VIP and octreotide. The ide ntity of the VIP binding site in the tumor was analyzed by Northern bl otting and revealed the expression of somatostatin receptor subtype 3, which binds both somatostatin-14 and VIP with higher affinity than oc treotide. Iodine-123-VIP scintigraphy would be an effective tracer to identity the tumor site in VMS patients.