Clinical value of whole body [18F]FDG-PET/CT in the detection of metastatic medullary thyroid cancer

Objectives To evaluate the value of whole-body [18F]FDG-PET/CT in the detection of metastatic medullary thyroid cancer.

Methods From November 2006 to November 2012, 50 medullary thyroid cancer patients (median age 48.7 years old, range 18-76) who had a total thyroidectomy operation underwent whole body [18F]FDG-PET/CT scans. The diagnostic accuracy of [18F]FDG-PET/CT was determined through both organ-based and patient-based analyses. Further pathological tests were performed on all identified lesions or clinically followed for a minimum period of 6 months.

Results One hundred and forty-four suspicious lesions were identified by organ-based analysis. Of these lesions, [18F]FDG-PET/CT detected 99 true positive lesions, sensitivity was 73%, specificity 66.7%. On the patient-based analysis, the overall sensitivity and specificity was calculated as 65.7% and 92.3%, respectively. Using a cut-off calcitonin value of 1000 pg/ml, in patients with calcitonin lower than this value, sensitivity and specificity were 42.9% and 91.0% respectively. In patients with calcitonin exceeding this value, they raised to 77.3% (χ2 = 4.392, P < 0.05) and 100% (χ2 =0.197, P > 0.05), respectively. Compared with conventional imaging modality, PET/CT scans detected more lesions in 10 patients (20.4%) and correctly changed the treatment in 8 patients (16.3%).

Conclusions [18F]FDG-PET/CT has excellent sensitivity and specificity especially when the calcitonin value is higher than 1000 pg/ml for detecting metastatic medullary thyroid cancer. Compared to conventional morphologic imaging methods, it provides additional information for diagnosis.