Supplementary Material for: Prognostic Value of Stimulated Thyroglobulin Levels at the Time of Radioiodine Administration in Differentiated Thyroid Cancer

Objective: The prognostic value of stimulated thyroglobulin (sTg) and Tg-related parameters prior to and immediately after radioactive iodine (RAI) administration was assessed in a cohort of patients presenting with differentiated thyroid cancer (DTC) as a predictor of recurrent or progressive structural disease. Methods: Clinical records of 180 DTC patients were retrospectively reviewed, and serum TSH, Tg, and Tg antibodies were recorded just before RAI administration (pre-) and at the time of whole body scanning (post-). Based on the results of initial staging and RAI scintigraphy, patients were divided into two groups: those who were considered to be structurally disease-free after thyroidectomy and RAI (group 1) and those who were not (group 2). Univariate analyses were performed for pre-Tg, ratioTg (post-Tg/pre-Tg), and other clinical and pathological markers for long-term outcome, as well as separate bivariate analyses focusing on pre-Tg to correct for possible confounders. Different pre-Tg cut-off values for predicting structural disease recurrence were assessed in a subgroup of patients in group 1 prepared with thyroid hormone withdrawal. Results: In group 1, (n = 166) male gender, higher T-stage and both Tg-related parameters proved to be significant risk factors for structural disease relapse. Of all candidate variables, only higher T-stage served to predict progressive structural disease in group 2 (n = 14). Subgroup analysis showed a negative predictive value of 91.67% for pre-Tg < 10 µg/L. Conclusion: The sTg value at the time of RAI administration may be helpful in predicting structural disease recurrence in patients with DTC.