The value of fluorine-18 fluorodeoxyglucose PET in patients with medullarythyroid cancer

The early detection of metastases from medullary thyroid cancer (MTC) is im portant because the only curative therapy consists in surgical removal of a ll tumour tissue. There is no single sensitive diagnostic imaging modality for the localization of all metastases in patients with MTC. Therefore, in many cases several imaging modalities (e.g. ultrasonography, magnetic reson ance imaging, computerized tomography and scintigraphy using pentavalent te chnetium-99m dimercaptosuccinic acid, thallium-201 chloride, indium-lll pen tetreotide, anti-CEA antibodies or metaiodobenzplguanidine) must be perform ed consecutively in patients with elevated calcitonin levels until the tumo ur is localized. In this prospective study, we investigated the value of fl uorine-18 fluorodeoxyglucose positron emission tomography ([F-18]FDG PET) i n the follow-up of patients with MTC. [F-18]FDG PET examinations of the nec k and the chest were performed in 20 patients with elevated calcitonin leve ls or sonographic abnormalities in the neck. Positive [F-18]FDG findings we re validated by histology, computerized tomography or selective venous cath eterization. [F-18]FDG PET detected tumour in 13/17 patients (nine cases we re validated by histology, four by computerized tomography). Five patients showed completely negative PET scans (of these cases, one was true-negative and four false-negative). One patient with [F-18]FDG accumulation in pulmo nary lesions from silicosis and one patient with a neck lesion that was not subjected to histological validation had to be excluded. Considering all v alidated localizations, [F-18]FDG PET detected 12/14 tumour manifestations in the neck, 6/7 mediastinal metastases, 2/2 pulmonary metastases and 2/2 b one metastases. In two patients with elevated calcitonin levels, no diagnos tic modality was able to localize a tumour. The sensitivity of [F-18]FDG PE T in the follow-up of MTC was 76% (95% confidence interval 53%-94%); this i s encouraging. [F-18]FDG PET promises to be a valuable diagnostic method, e specially for the detection of lymph node metastases, surgical resection of which can result in complete remission.