Abstract
PURPOSE: To evaluate the value of thyroglobulin doubling time (Tg-DT) in predicting (18)F-FDG PET/CT findings and clinical outcomes in differentiated thyroid cancer (DTC) patients with high thyroglobulin (Tg) level and negative (131)I whole-body scan ((131)I WBS). MATERIALS AND METHODS: 188 DTC patients with Tg levels ≥ 10 ng/ml and negative (131)I WBS underwent (18)F-FDG PET/CT scan. Three last consecutive values of unstimulated Tg were used to calculate Tg doubling time (Tg-DT). ROC curve analysis was performed to determine the optimal thresholds of Tg-DT in predicting (18)F-FDG PET/CT results. Patients were followed up for at least 12 months after PET/CT scan. The Kaplan-Meier curve was used to estimate progression-free survival (PFS) and overall survival (OS). Cox regression analyses were conducted to identify factors significantly associated with PFS and OS. RESULTS: The specificity and positive predictive value of Tg-DT for predicting (18)F-FDG PET/CT findings were 93.94%, and 92.6%, respectively, while those for Tg levels were 78.79% and 83.53% (p < 0.001). This study revealed that stimulated Tg and Tg-DT can predict disease progression and survival in DTC patients. Age > 55, distant metastasis on (18)F-FDG PET/CT, and Tg-DT ≤ 12 months were independent predictors of PFS. Distant metastasis and Tg-DT ≤ 12 months were independent prognostic factors for OS. CONCLUSION: Tg-DT is a valuable biomarker in predicting positive (18)F-FDG PET/CT findings in DTC patients with high Tg level and negative (131)I WBS. Along with distant metastases, Tg-DT ≤ 12 months is the only independent prognostic factor for PFS and OS.