LIMITED VALUE OF F-18 FLUORODEOXYGLUCOSE POSITRON-EMISSION-TOMOGRAPHYFOR THE IMAGING OF NEUROENDOCRINE TUMORS

Scintigraphy using [In-111-DTPA-D-Phe(1)]-pentetreotide or pentavalent technetium-99m-dimercaptosuccinic acid [Tc-99m(V)-DMSA] has been show n to localize well-differentiated and slowly growing neuroendocrine tu mours, whereas increased fluorodeoxyglucose (FDG) uptake is associated with malignancy. The aim of this study was to compare the value of fl uorine-18 FDG positron emission tomography (PET) with that of somatost atin receptor scintigraphy (SS-R) and dual-radionuclide scintigraphy [ SS-R and Tc-99m(V)-DMSA = DNS] in detecting malignant neuroendocrine r umours. Fifteen patients with metastasizing gastroenteropancreatic tum ours (GEP tumours; n = 7), medullary thyroid carcinomas (MTCs; n = 8) and elevated tumour markers [GEP rumours: 5-hydroxyindoleacetic acid, insulin; MTCs: calcitonin, carcinoembryonic antigen (CEA)] were studie d. Prior to PET, all patients with GEP tumours underwent SS-R. DNS was performed in all patients with MTC. Patients had been fasting for at least 12 h and normal glucose plasma levels were confirmed. Sixty minu tes after intravenous administration of F-18-FDG (mean: 374 MBq) whole -body PET and regional scans were performed. In addition, the resected tissues were prepared for immunocytochemistry examination (cell cycle -associated Ki-67 antigen). In two patients with less-differentiated G EP tumours associated with high proliferative activity and increased F DG uptake, SS-R failed to detect any lesion. In comparison, in four pa tients with well-differentiated GEP rumours showing low proliferative activity, SS-R localized four primary tumours, 22 lymph node metastase s and 18 malignant liver lesions, whereas F-18-FDG PET demonstrated no rmal distribution, In one patient with a metastasizing carcinoid (medi um proliferative activity) SS-R localized multiple metastases, whereas PET demonstrated low FDG uptake in all known metastases. In patients with recurrent MTC and rapidly increasing CEA levels DNS detected only three lesions in two patients, whereas PET demonstrated one pulmonary , three osseous, 20 mediastinal, ten locoregional, and four liver meta stases in seven patients. Twenty-nine malignant lesions were confirmed by follow-up and nine lymph node metastases could be surgically remov ed. In conclusion, PET imaging of gastroenteropancreatic tumours revea led increased glucose metabolism only in less-differentiated GEP tumou rs with high proliferative activity and metastasizing MTC associated w ith rapidly increasing CEA levels. Therefore, additional F-18-FDG PET should be performed only if SS-R or DNS is negative.