Hashimoto thyroiditis is associated with the efficacy of low dose (30 mCi) radioiodine ablation in differentiated thyroid cancer

Abstract

Background: Radioactive iodine (RAI) ablation is considered in the postsurgical management of differentiated thyroid carcinoma (DTC). The aim of this study was to investigate the effectiveness of low dose (30 mCi) RAI ablation and the factors associated with RAI success. Methods: A retrospective study was conducted on 691 patients who received low dose RAI ablation after total thyroidectomy. The success of the first RAI ablation was defined as no remnant on the whole body scan with preablative stimulated thyroglobulin (s-Tg) <2.0ng/ml at the second time of RAI administration. Patient demographics, pathologic features, laboratory test, and RAI ablation result were collected. Results: Low dose RAI ablation was successful in 431 patients (62.3%) after the first RAI therapy. The first RAI failure was associated with multiplicity (39.3% vs 47.1%, p=0.045) and bilaterality (23.1% vs 30.1%, p=0.041) of primary tumor, coexisting Hashimoto thyroiditis (HT

25.5% vs 40.8%, p<0.001), and higher s-Tg level (1.5±2.4 vs 6.5±19.0, p<0.001). There were no significant differences in age, sex, and pathologic features of tumor including size. On multivariate analyses, both coexisting HT and preablative s-Tg retained statistical significance. The relative risk (RR) of first RAI failure with coexisting HT was significantly increased at 2.86 (95% confidence interval [CI] 1.95, 4.17, p<0.001). The RR along preablative s-Tg level was also increased, with an RR of 1.23 (95% CI 1.15, 1.31, p<0.001). Conclusions: Success of low dose RAI ablation at the first time was influenced by coexisting HT. Further investigation about the relation of HT and RAI ablation is warranted.