Detection of distant metastasis at the time of ablation in children with differentiated thyroid cancer: the value of pre-ablation stimulated thyroglobulin.

Background The present study was designed to determine the value of pre-ablation stimulated thyroglobulin (s-Tg) in predicting distant metastasis (DM) at the time of ablation in children with differentiated thyroid cancer. Methods From August 2009 to December 2016, consecutive children with differentiated thyroid cancer undergoing remnant ablation were retrospectively analyzed. Serum s-Tg was measured with the high-sensitive electrochemiluminescence immunoassay during hypothyroidism at ablation just before the ablative radioactive iodine (131I) administration. Post-ablation, whole body planar scintigraphy was obtained 5 days after administration of ablation activity of 131I. Single photon emission computed tomography/low-dose computed tomography (SPECT/CT) was added for children whose planar findings were inconclusive. Receiver-operating characteristics (ROC) curve analysis was employed to find a cut-off level of pre-ablation s-Tg as a predictor of DM at the time of ablation. Results Fifty-seven children were included for the analysis. Metastases were noticed on post-ablation scintigraphy in 20 (35%) children: five post-operative residual neck lymph node metastases, four post-operative residual neck lymph node and lung metastases, three mediastinal lymph node and lung metastases and eight lung metastases. A significant difference in pre-ablation s-Tg levels was found in children with DM compared with those without DM, 603.5 vs. 5.7 ng/mL, respectively. A pre-ablation s-Tg level of 156 ng/mL was established as the optimal cut-off point to predict DM. Conclusions This study demonstrated that pre-ablation s-Tg could potentially act as a predictor of DM at the time of ablation in children with differentiated thyroid cancer. We also propose a specific pre-ablation s-Tg cut-off value of 156 ng/mL as an optimal threshold for practical use.