Stimulated serum thyroglobulin but not RAIU level is a prognostic factor for ablation efficacy with a 3.7GBq (100mCi) fixed 131I dose in patients with differentiated thyroid cancer.

Abstract

OBJECTIVE\nThe aim of this study was to determine prognostic value of radioactive iodine uptake (RAIU) and stimulated thyroglobulin (sTg) regarding the ablation efficacy in patients with differentiated thyroid cancer.\n\n\nSUBJECTS AND METHODS\nWe studied 466 differentiated thyroid cancer (DTC) patients without distant 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: 1) sTg<2ng/mL, 2) 2ng/mL≤sTg<5ng/mL, 3) 5ng/mL≤sTg<10ng/mL and 4) sTg≥10ng/mL subgroup. The ablation success was defined as a negative scan 6 months to 1 year and other imaging like US did not detect anything suspicious after ablation. Excellent response was considered as: sTg<1ng/mL with negative thyroglobulin antibodies (TgAb) and negative image scans.\n\n\nRESULTS\nThe rate of successful ablation was 88.3%, 88.7%, 88.4% and 79% between group A to D, 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 group A to D. 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 A, respectively (P<0.001). Similarly, there was a significant difference about excellent response rate between subgroups 1 to 4 for groups B, C and D.\n\n\nCONCLUSION\nAfter total thyroidectomy, not RAIU but sTg is a prognostic factor for ablation efficacy with a 3.7GBq (100mCi) fixed 131I dose in patients with DTC.