Impact of F-18-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) in patients with biochemical evidence of recurrent or residual medullary thyroid cancer

Background: Conventional imaging such as with Tc-99m(V)dimercaptosunnic acid (DMSA), In-111-octreotide scintigraphy, computed tomography (CT), and magnetic resonance imaging (MRI) rarely localizes occult medullary thyroid cancer (MTC). The role of F-18-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) is not well defined. The aim of this study was to examine the usefulness of postoperative FDG-PET in localizing MTC metastases.Methods: FDG-PET was performed in 26 patients with elevated serum tumor markers after total thyroidectomy with central compartment dissection and additional neck dissection on indication. Patient- and lesion-based results were compared with the findings of conventional nuclear imaging and validated by morphological imaging (CT, MRI, ultrasonography), including bone scintigraphy and pathology when possible. Clinical impact was evaluated.Results: FDG-PET detected foci in 50% of patients with lesion-based sensitivity of 96%. In-111-octreotide detected foci in 19% with sensitivity of 41%, and Tc-99m(V)DMSA scintigraphy and morphological imaging detected foci in 21% and 40%, respectively, with sensitivity of 57% and 87%. No lesions were found in 11 patients (42%). Positive FDG-PET findings led to surgical intervention in nine patients (35%). They all underwent surgery for removal of residual tumor or metastases. One patient achieved disease-free status. In all patients who underwent surgery, serum calcitonin levels were reduced by an average of 58 +/- 31%.Conclusions: For detection of occult MTC lesions, FDG-PET is superior to conventional nuclear imaging and is the best detection method yet available. FDG-PET in postoperative follow-up has clinical value and may be used for guiding reoperation and additional morphological imaging preoperatively.