Not radioactive iodine-131 uptake but thyroglobulin was a prognostic factor for ablation efficacy in non-metastaticthyroid cancer

Objectives: The aim of this study was to determine the relationship between radioactive iodine uptake (RAIU) and serum thyroglobulin (sTg) versus the efficacy of ablation of post-surgical remnants, in patients with differentiated thyroid cancer. Subjects and Methods: We studied 466 patients without metastases after thyroidectomy who underwent iodine-131 (¹³¹I) ablation and were pre-therapy assessed by RAIU. The patients were divided into four groups according to the RAIU result, including: a) RAIU<2%, b) 2%≤RAIU<5%, c) 5%≤RAIU<10% and d) RAIU≥10%. Every group was divided into four subgroups according to sTg levels, namely: a) sTg<2ng/mL, b) 2ng/ml≤sTg<5ng/mL, c) 5ng/ml≤sTg<10ng/mL and d) sTg≥10ng/mL subgroup. Successful therapy was defined as a negative scan 6 months to 1 year after ablation. Excellent response was considered as: sTg<1ng/mL with negative thyroglobulin antibodies (TgAb) and negative image scans.

Results: The rate of successful ablation was 88.3%, 88.7%, 88.4% and 79% for the four groups, respectively (P=0.779). There was also no significant difference about the excellent response rate (64.5% vs 63.6% vs 48.8% vs 57.1%, P=0.256) between groups 1 to 4. The ablation success rate did not differ significantly between subgroups 1 to 4 in every group. However, the rates of excellent response were 86.8%, 52.1%, 25% and 15.2% between subgroups 1 to 4 for group 1, respectively (P=0.000). Similarly, there was a significant difference about excellent response rate between subgroups 1 to 4 for groups 2, 3 and 4.

Conclusions: After total thyroidectomy, RAIU levels had no influence on the efficacy of ablation and sTg was the only factor to determine the ablation efficacy.