Re-ablation I-131 activity does not predict treatment success in low- and intermediate-risk patients with differentiated thyroid carcinoma

Prpić, Marin and Kruljac, Ivan and Kust, Davor and Kirigin, Lora S. and Jukić, Tomislav and Dabelić, Nina and Bolanča, Ante and Kusić, Zvonko (2016) Re-ablation I-131 activity does not predict treatment success in low- and intermediate-risk patients with differentiated thyroid carcinoma. Endocrine, 52 (3). pp. 602-608. ISSN 1355-008X

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Abstract

The aim of this study was to evaluate the efficacy of different radioactive iodine (I-131) activities used for re-ablation, to compare various combinations of treatment activities, and to identify predictors of re-ablation failure in low- and intermediate-risk differentiated thyroid carcinoma (DTC) patients. The study included 128 consecutive low- and intermediate-risk patients with DTC with ablation failure after total thyroidectomy. Patient characteristics, T status, tumor size, lymph node involvement, postoperative remnant size on whole-body scintigraphy, serum thyroglobulin (Tg), thyroid-stimulating hormone (TSH), anti-Tg antibody (TgAb), and Tg/TSH ratio were analyzed as potential predictors of the re-ablation success. Re-ablation was successful in 113 out of 128 patients (88.3 %). Mean first I-131 activity was 2868 ± 914 MBq (77.5 ± 24.7 mCi) and mean second I-131 activity 3004 ± 699 MBq (81.2 ± 18.9 mCi). There was no association between the first, second, and cumulative activity with re-ablation treatment outcome. Treatment failure was associated with higher Tg levels prior to re-ablation (Tg2) (OR 1.16, 95 % CI 1.05-1.29, P = 0.003) and N1a status (OR 3.89, 95 % CI 1.13-13.41, P = 0.032). After excluding patients with positive-to-negative TgAb conversion, Tg2 level of 3.7 ng/mL predicted treatment failure with a sensitivity of 75.0 %, specificity of 80.5 %, and a negative predictive value of 97.1 %. Patients with positive-to-negative TgAb conversion had higher failure rates (OR 2.96, 95 % CI 0.94-9.29). Re-ablation success was high in all subgroups of patients and I-131 activity did not influence treatment outcome. Tg may serve as a good predictor of re-ablation failure. Patients with positive-to-negative TgAb conversion represent a specific group, in whom Tg level should not be used as a predictive marker of treatment outcome.

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