Clinical implication of preablation thyroglobulin level in differentiated thyroid carcinoma patients underwent recombinant human thyrotropin aided ablative radioiodine treatment

Objectives The aim of this study was to compare serum thyroglobulin (Tg) level measured just before and after recombinant human thyrotropin (rhTSH)-aided radioiodine ablative treatment (RIT) for predicting treatment response in patients with differentiated thyroid carcinoma (DTC).

Methods We enrolled 89 patients with DTC who underwent rhTSH-aided RIT (2.9-6.7 GBq) after total thyroidectomy. Serum Tg level was measured two times: 24 hours (early Tg) and 72 (or 96) hours (delay Tg) after the 2^nd rhTSH injection. Excellent response was determined by the stimulated Tg levels <1 ng/mL with negative radioiodine uptake or suppressed Tg levels <0.2 ng/mL with negative neck ultrasonography after 8.3 ± 2.3 months of RIT. Univariate and multivariate analyses were done for early Tg, delay Tg, delta Tg (delay Tg - early Tg), ratio Tg (delay Tg: early Tg ratio), and other clinical and pathological variables (sex, age, TNM stage, tumor size, multicentricity, bilaterality, I-131 dose).

Results There were 44 (49.4%) excellent response patients. Univariate analysis showed that small tumor size (P=0.029), low early Tg levels (P=0.018) were significantly associated with excellent response. By multivariate analysis, early Tg level proved as the only independent predictor of excellent response (odds ratio [OR] = 1.944; 95% CI =1.167-3.240; P=0.011). Continuous variables (tumor size, early Tg and delay Tg) were stratified by cut-off values, according to ROC curve analysis. Of three candidate variables, early Tg level (OR = 17.854; 95% CI =2.711-117.582; P=0.003) only showed significance in predicting excellent response.

Conclusions Our data shows that the early Tg level may be used as a new prognostic indicator of treatment response in patients with DTC who underwent rhTSH-aided RIT. Tg should be measured just before RIT in rhTSH-aided RIT patients.