Role of [18F]FDG-PET/CT in the detection of occult recurrent medullary thyroid cancer

PURPOSEMany patients with medullary thyroid carcinoma (MTC) have persistently elevated calcitonin levels after initial treatment, indicating disease recurrence. Conventional imaging is often negative or shows equivocal findings. In this study we report our experience with 2-deoxy-2-[F]fluoro-D-glucose positron emission tomography/computed tomography ([F]FDG-PET/CT) in the evaluation of this specific group. METHODSBetween February 2007 and May 2009, 38 [F]FDG-PET/CT scans were performed on 32 patients with MTC and elevated calcitonin levels for localization of recurrent disease. Six of these patients had a second [F]FDG-PET/CT scan. RESULTSAmong the 38 [F]FDG-PET/CT scans there were 18 positive and 20 negative scans. Out of the 18 positive scans, 17 were true positive and one false positive. These findings suggest that [F]FDG-PET/CT provides additional information in almost half of all cases (overall per patient sensitivity of 47.4%) but using a serum calcitonin cut-off of 1000 pg/ml this rate is increased to 80%. An interesting finding of the study was that none of the six patients with multiple endocrine neoplasia type IIA syndrome had a positive [F]FDG-PET/CT scan for MTC. When these patients were excluded, the overall per patient sensitivity rose to 60% and in patients with calcitonin levels >1000 pg/ml this rate increased to 100%. The mean SUVmax of all lesions showing [F]FDG uptake was 3.96±1.61 (range, 2–7). CONCLUSION[F]FDG-PET/CT seems to be valuable for the detection of recurrence in patients with highly elevated calcitonin levels and negative conventional imaging findings. In addition, it seems that the sensitivity of [F]FDG-PET/CT may be higher in patients with sporadic or familial MTC than in patients with MTC as part of multiple endocrine neoplasia type IIA syndrome.