The relationship between thyroglobulin, thyroglobulin doubling time and recurrent/metastatic lesions detected in 18F-FDG PET/CT in radioiodine refractory differentiated thyroid cancer

Abstract

Background: 18F-FDG PET/CT is method with high sensitivity and specificity in the diagnosis of recurrent lesions in patients with radioiodine refractory differentiated thyroid cancer ((RAI-R- DTC). The aim of this study was to evaluate the relationship between Tg, Tg – DT and rucurrent/metastatic lessions detected in 18F-FDG PET/CT imaging in RAI-R DTC patients.

Methods: 119 RAI-R DTC patients underwent 18F-FDG PET/CT. At least two consecutive Tg measurements under the thyroid hormone replacement therapy (TSH ≤ 0,1 uIU/ml) to calculate Tg - DT before 18F-FDG PET/CT scan. We analyzed the relationship between PET/CT imaging and clinical characteristics, risk of recurrence, Tg and Tg – DT.

Results: 18F-FDG PET/CT imaging detected recurrent lesions in 88 patients (73,9 %) and distant metastasis in 29 patient (24,3 %). Tg-DT was significantly lower in the positive PET/CT group compared to negative PET/CT group (median 12.9 vs 166 months, p< 0.001). Serum Tg concentration in the patients with distant metastasis was higher than those without distant metastasis (334 ng/ml vs 114.6 ng/ml, p < 0.001). In univariate and multivariate logistic regression analysis, Tg-DT was an independent predictor of positive PET/CT and serum Tg concentration was a predictor of distant metastasis. The ROC curve determines the optimal threshold of Tg - DT in predicting positive PET/CT is 34.75 months and Tg level at 218.1 ng/ml predicting distant metastasis

Conclusion: Tg - DT is reliable value in predicting positive 18F - FDG PET/CT and serum Tg concentration is valuable for predicting the outcome of distant metastasis in RAI – R DTC patients.