Abstract: Background and purpose: The response after initial treatment ［surgery + ¹³¹I + thyroid-stimulating hormone (TSH) suppression］ is critical for the dynamic assessment of the risk of recurrence in patients with differentiated thyroid cancer (DTC). This study aimed to investigate the potential value of preablative stimulated thyroglobulin (ps-Tg) of DTC patients in predicting the therapeutic response. Methods: Patients with a median follow-up of 74.5 months (136 patients) were divided into 4 groups according to the therapeutic response evaluation system: excellent response (ER) (86 patients), indeterminate response (IDR) (18 patients), biochemical incomplete response (BIR) (4 patients), and structural incomplete response (SIR) (28 patients). The χ² test, Fisher's exact test and Kruskal-Wallis test were used to evaluate the differences in basic clinicopathological features among the 4 groups. The receiver operating characteristic (ROC) curve was analyzed to evaluate the clinical value of ps-Tg and tumor size for predicting ER and the optimal cut-off point respectively. Multivariate analysis was used to quantify the independent factors of ER. The cumulative risk of non-excellent response curves according to ps-Tg and tumor size were constructed with the Kaplan-Meier method, and the log-rank test was used to compare these curves. Results: Significant differences in ps-Tg level, tumor size and extrathyroidal invasion could be observed among the 4 groups (P<0.05), while there was no significant difference in gender, age and cervical lymph node metastasis (P>0.05). The areas under the ROC curves of ps-Tg and tumor size for predicting ER were 0.865 and 0.666, respectively. A cut-off value of ps-Tg was obtained at 9.05 ng/mL, with high sensitivity and specificity of 83.7% and 80.0% respectively, and 1.05 cm of tumor diameter was set as the cut-off value with relatively low sensitivity and specificity of 53.5% and 72.0%, respectively. Multivariate analysis showed that ps-Tg and tumor size could be used as independent predictors of ER (OR=20.571, P=0.015; OR=3.291, P=0.008). With the increase of diameter, the non-ER risk of patients with ps-Tg≥9.05 ng/mL was significantly higher than that of the group with ps-Tg<9.05 ng/mL (P=0.000 3). Conclusion: ps-Tg (with a cut-off value of 9.05 ng/mL) could predict the ER in this cohort, and its combination with tumor size might better predict the non-ER response to initial treatment.

Key words: Differentiated thyroid carcinoma, Stimulated thyroglobulin, Radioiodine therapy, Response to therapy