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.

Abstract

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). 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 7months (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 >2ng/ml. We classified patients into three groups according to the value of preablation Tg (group 1, <1ng/ml; group 2, ≥1 and <10ng/ml; group 3, ≥10ng/ml) and compared clinical variables to therapeutic response. 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 ≥10ng/ml had 25.5 times greater chance of therapeutic failure than those with levels <10ng/ml (95% CI = 5.43-119.60; P < 0.001). A high preablation Tg level is the most significant predictor of therapeutic failure at the time of first HI-Rx in patients with PTC.