Thyroglobulin/thyrotropin ratio for predicting long-term response in differentiated thyroid carcinoma: a retrospective study

Abstract

Objective: Thyrotropin-stimulated thyroglobulin (STg) after total thyroidectomy is a prognosis marker for differentiated thyroid carcinoma (DTC). As Tg level is influenced by thyrotropin (TSH), perhaps the STg/TSH ratio is also a prognosis marker for these tumours. We aimed to compare STg/TSH ratio and first STg level in differentiated thyroid carcinoma patients for their ability to predict the long-term response to initial treatment.

Methods: This retrospective study evaluated data from 181 DTC patients for first (1^st) STg and STg/TSH ratio, at 1-3 months post-total thyroidectomy and before iodine-131 therapy, according to response to initial therapy [Excellent/Indeterminate or Incomplete (Biochemical/Structural)] observed at final evaluation, and with the survival time with excellent/indeterminate response.

Results: Cases with incomplete response presented higher STg level [225.13 ± 585.26 ng/mL versus (vs) 20.4 ± 192.9 ng/mL; p < 0.001] and STg/TSH ratio (3.01 ± 7.8 vs 0.27 ± 2.58; p < 0.001). Cutoffs of 5 ng/mL for STg and 0.085 for STg/TSH displayed sensitivities of 76.7% and 76.9%, and specificities of 79.2% and 82.6%, respectively, in predicting response to therapy. Values below these cutoffs were associated with longer survival time in excellent/indeterminate response (140.4 vs 15.9 and 144.6 vs 15.9 months, respectively).

Conclusion: STg/TSH ratio has a similar performance to the 1^st STg in predicting long-term response to initial therapy.

Keywords: Thyroid neoplasms; prognosis; thyroglobulin.

Figure 1. Receiver-operating characteristic (ROC) curves of the first stimulated thyroglobulin [A: cutoff = 5.0 ng/mL ng/mL (area under the curve: 0.907; p < 0.001)] and regarding first stimulated thyroglobulin/thyroid-stimulating hormone ratio [B: cutoff = 0.085 (area under the curve: 0.920; p < 0.001)] as predictors of incomplete response (biochemical and/or structural) in the last evaluation.

Figure 2. Kaplan-Meyer curves to assess patient survival time in excellent/indeterminate response, using the cutoff point established for the first stimulated thyroglobulin – STg as variable (A: mean survival with STg ≥ 5 ng/mL = 15.9 months and with STg < 5 ng/mL = 140.4 months; Log Rank < 0.001) and for the first stimulated thyroglobulin/thyrotrophin – STg/TSH ratio (B: mean survival with STg/TSH ≥ 0.085 = 15.9 months and with STg/TSH < 0.085 = 144.6 months; Log Rank < 0.001) in the last evaluation as predictors of outcome.