Endocrine Abstracts

Introduction: Differentiated thyroid cancer (DTC) is the most frequent endocrine cancer. After surgery followed, if any, by ¹³¹I radio remnant ablation (RRA), follow-up monitoring consists of neck ultrasonography (US) and measurements of thyroglobulin (Tg) levels and anti-Tg antibodies (Ac-Tg) both on levothyroxine (L-T₄) therapy and after recombinant TSH (rTSH). The aim of our study is to define a cut-off of Tg before RRA (RRA-Tg) during L-T₄ withdrawal predictive of remission of disease.

Materials and methods: We prospective evaluated 113 patients who underwent total thyroidectomy with or without lymphadenectomy for DTC. All patients received RRA after surgery, without evidence of iodine uptake outside neck. Ac-Tg were negative. Tg after rTSH stimulation (rTSH-Tg) was performed 9–12 months after RRA. During follow-up patient was considered ‘free of disease’ on the basis of undetectable Tg values on suppressive L-T₄ therapy (L-T₄-Tg), rTSH-Tg < 2 ng/ml, negative Ac-Tg and negative neck US.

Results: RRA-Tg was between 0.5 and 117 ng/ml (mean±S.D.: 7.52±14.06); L-T₄-Tg was between 0.01 and 1.00 ng/ml (mean±S.D. 0.15±0.20); rTSH-Tg was between 0.02 and 15.00 ng/ml (mean±S.D.: 0.58±2.06). 107 patients (94.7%) showed rTSH-Tg ≤2 ng/ml; six patients (5.3%) had rTSH-Tg ≥2 ng/ml. ROC curve demonstrated that RRA-Tg can be considered highly predictive of negative rTSH-Tg. In particular, for RRA-Tg values of 10 ng/ml sensitivity and specificity are of 100 and 83% respectively; for RRA-Tg values of 18.35 ng/ml sensitivity and specificity are of 100 and 95% respectively.

Conclusions: RRA-Tg can be considered an accurate parameter to predict the remission of DTC. For RRA-Tg values <18.35 ng/ml, during subsequent follow-up the possibility to avoid rTSH-Tg test should be considered in presence of undetectable L-T₄-Tg levels, negative Ac-Tg and negative neck US.