The clinical role of FDG PET in patients with recurrent medullary thyroid carcinoma

1655 Objectives: Medullary carcinoma is a tumor of parafollicular C-cells in the thyroid gland. Its prognosis is poor and recurrence is relatively common after initial treatment. The only curative treatment is the removal of tumor tissue and therefore, early detection of recurrent disease may lead curative surgical intervention and optimal outcome. No single imaging modality has been shown to localize all tumor sites accurately. In this study we assessed the role of FDG PET in detecting recurrent medullary thyroid carcinoma (MTC). Methods: Seventeen FDG PET scanning were performed in 16 MTC patients (11 male, 5 female, age range 13-80). In this population either there was a clinical suspicion of recurrence due to elevated serum calcitonin levels (range; 66.7-60962.6 ng/ml) or a positive radiological finding on a routine follow up study. A second PET study was performed for restaging after radical neck dissection in one patient. PET imaging was acquired one-hour following intravenous administration of FDG. Positive findings were correlated with those of histopathological and the conventional imaging procedures. Results: FDG PET revealed 26 sites of hypermetabolic foci in 13 cases and 11 of these proved to be true positive. There were two false positive results; a lymph node with reactive changes in the neck and an inflammatory lesion in right distal arm. All procedures including serum calcitonin measurement and PET were negative in one patient who underwent a second PET imaging after cervical dissection. In 3 patients with elevated serum calcitonin levels, all imaging modalities including FDG PET were negative and no clear-cut explanation was found for the abnormal laboratory results. The overall sensitivity of FDG PET was 78.5%. Conclusions: FDG PET appears to complement other imaging modalities in detecting of MTC recurrence. As such, it may improve the outcome of patients with this cancer following radical surgery and during the course of the disease when recurrence is suspected.