To explore the value of preablative stimulated thyroglobulin (ps-Tg) in predicting distant metastasis (DM) at the time of ¹³¹I therapy in children and adolescents with differentiated thyroid cancer (DTC).

From January 2016 to March 2020, 54 children and adolescents who underwent total thyroidectomy due to DTC in Peking Union Medical College Hospital were retrospectively reviewed and divided into 2 groups according to the presence of DM or not: M0 group(n=29, 10 males, 19 females, age (16.3±3.8) years) and M1 group(n=25, 13 males, 12 females, age (12.4±4.3) years). Independent-sample t test, χ² test (or Fisher′s exact test) and Mann-Whitney U test were used to analyze the general characteristics between the two groups. According to status of regional lymph node (RLN) at the time of ¹³¹I therapy, the two groups were further divided into M1RLN+ (n=8) and M1RLN-(n=17), M0RLN+ (n=5) and M0RLN-(n=24) subgroups. Mann-Whitney U test was used to analyze the different ps-Tg levels between M0 and M1, M1RLN+ and M1RLN-, as well as M0RLN+ and M0RLN-groups. The receiver operating characteristic (ROC) curve analysis was employed to obtain a cut-off value of ps-Tg as a predictor of DM.

Patients with DM tended to have higher ps-Tg level (medians: 406.80 μg/L vs 7.90 μg/L, U=690.000, P<0.001), younger age (t=-3.559, P=0.001), larger tumor size (t=3.523, P=0.001), more advanced T stage (U=506.500, P=0.010) and more multifocality(P=0.013) in comparison with those without DM. Though ps-Tg did not significantly differ between M1RLN+ group and M1RLN-group (U=98.500, P>0.05) or between M0RLN+ group and M0RLN-group (U=63.000, P>0.05), the two RLN+ groups tended to hold higher medians than the two RLN-groups (18.05vs 5.71 μg/L; 1 698.50 vs 216.40 μg/L). In order to avoid the possible influence on the ps-Tg cut-off value, 13 RLN+ samples were removed, and the area under the ROC curve was 0.946 (95% CI: 0.883-1.000). The ps-Tg level of 55.87 μg/L was established as the optimal cut-off value to distinguish M0RLN- from M1RLN-, with the sensitivity and specificity of 14/17 and 95.8%(23/24), respectively.

Ps-Tg holds a high predictive value in identifying DM, which may be of great help in avoiding inadequate ¹³¹I treatment in children and adolescents with metastatic DTC ignored by radiological examinations.

Thyroid neoplasms; Neoplasm metastasis; Thyroglobulin; Radiotherapy; Iodine radioisotopes; Child; Adolescent