The Use of (18)F-FDG PET/CT in Patients with Recurrent Differentiated Thyroid Cancer

OBJECTIVES: (18)Fluorine-fluorodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) is used to monitor the recurrence in thyroid cancer patients when there is suspicion of metastases. De-differentiated lesions become (18)F-FDG avid with a more aggressive clinical course. The aim of this study was to investigate the use of (18)F-FDG PET/CT in differentiated thyroid cancer. METHODS: Forty-six patients, either with a negative radioiodine scan or clinical progression and suspicions for metastases with differentiated thyroid cancer that were referred to our department for (18)F-FDG PET/CT scan and evaluated retrospectively. PET/CT findings were correlated with clinical and histopathological findings, serum thyroglobulin (Tg), and anti-Tg levels. RESULTS: Twenty-six patients (56.2%) were positive for recurrence in (18)F-FDG PET/CT images. Positive (18)F-FDG PET/CT findings were significantly correlated with the disease stage and Tg levels. Maximum standardized uptake value did not correlate with other findings or patients’ profiles. The cut-off value for Tg was at 52.5 ng/mL having 73.08% sensitivity, 75% specificity, 79.17% positive predictive value, and 68.18% negative predictive value for (18)F-FDG PET/CT imaging. CONCLUSION: (18)F-FDG PET/CT is useful for detecting recurrence in differentiated thyroid cancer. Increased Tg levels and stage of the disease were significantly correlated with (18)F-FDG positivity. (18)F-FDG positivity may also provide information about the de-differentiation process that may support the treatment plan.