The role of Tg kinetics in predicting 2-[18F]-FDG PET/CT results and overall survival in patients affected by differentiated thyroid carcinoma with detectable Tg and negative 131I-scan
Domenico Albano, Mark Tülchinsky, Francesco Dondi, Angelica Mazzoletti, Francesco Bertagna, Raffaele Giubbini
Abstract
Abstract Purpose The aim of this study was to assess the potential role of thyroglobulin (Tg) kinetics in predicting 2-[ 18 F]-FDG-PET/CT results and overall survival (OS) in patients affected by differentiated thyroid carcinoma (DTC) and suspected recurrence. Methods On hundred and thirty-nine patients were retrospectively included. All patients underwent 2-[ 18 F]-FDG-PET/CT due to detectable Tg levels and negative [ 131 I] whole-body scan. The last two consecutive serum Tg measurements before PET/CT were used for Tg-doubling time (TgDT) and Tg-velocity (Tg-vel) calculation. Receiver operating characteristic (ROC) curves were used to determine the optimal cutoff points for Tg, TgDT and Tg-vel for predicting PET/CT results. Results One hundred and fifteen (83%) patients had positive PET/CT for DTC recurrence, while the remaining 24 (17%) negative. Stimulated Tg before PET and Tg-vel were significantly higher in patients with a positive PET/CT scan than negative scan (average Tg 190 vs 14 ng/mL, p = 0.006; average Tg-vel 4.2 vs 1.7 ng/mL/y, p < 0.001). Instead, TgDT was significantly shorter in positive scan (average TgDT 1.4 vs 4.4 years, p < 0.001). ROC curve analysis revealed the best Tg, TgDT and Tg-vel cutoff of 18 ng/mL,1.36 years and 1.95 ng/mL/y. In patients with Tg<18 ng/mL, the PET/CT detection rate was significantly lower in patients with low Tg-vel ( p = 0.018) and with long TgDT ( p = 0.001). ATA class risk, PET/CT results and Tg before PET were confirmed to be independent prognostic variables for OS. Conclusions Tg kinetics may help to predict 2-[ 18 F]-FDG-PET/CT results in DTC patients with negative [ 131 I]WBS and detectable Tg, especially in case of low-moderate Tg.