Stimulated Serum Thyroglobulin Level at the Time of First Dose of Radioactive Iodine Therapy Is the Most Predictive Factor for Therapeutic Failure in Patients With Papillary Thyroid Carcinoma.

Purpose: To investigate the clinical importance of serum thyroglobulin (Tg) levels just before high-dose I-131 ablation therapy (preablation Tg) for predicting therapeutic failure in patients with papillary thyroid carcinoma (PTC).

Methods: Patients with PTC (n = 132) undergoing total thyroidectomy followed by the first high-dose I-131 ablation therapy (HI-Rx) were included in this retrospective review. Just before HI-Rx, preablation Tg, anti-Tg antibody, and TSH were measured. The patients were followed up for a mean period of 7 months (range 6-23 months) by I-123 whole-body scans (f/u IWBS) and stimulated Tg (f/u Tg). Therapeutic failure was defined by positive f/u IWBS or f/u Tg >2 ng/ml. We classified patients into three groups according to the value of preablation Tg (group 1, <1 ng/ml; group 2, ≥1 and <10 ng/ml; group 3, ≥10 ng/ml) and compared clinical variables to therapeutic response.

Results: Therapeutic failure was noted in 39 patients (29.5 %). On univariate analysis, T stage, tumor size, and preablation Tg were the statistically significant factors that could predict therapeutic failure. After multivariate analysis, preablation Tg was the only independent predictor of therapeutic failure (P < 0.001). The therapeutic failure rate was significantly increased as the preablation Tg level increased (11.3 %, 33.3 %, and 87.5 % in groups 1, 2, and 3, respectively; P < 0.001). Individuals with preablation Tg levels ≥10 ng/ml had 25.5 times greater chance of therapeutic failure than those with levels <10 ng/ml (95 % CI = 5.43-119.60; P < 0.001).

Conclusions: A high preablation Tg level is the most significant predictor of therapeutic failure at the time of first HI-Rx in patients with PTC.