Postoperative Radioactive Iodine Ablation Effective in Reducing Disease Recurrence in Low-Risk Thyroid Cancer

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The use of radioactive iodine in patients at low risk for recurrence of thyroid cancer should be carefully assessed to minimize risk.
The use of radioactive iodine in patients at low risk for recurrence of thyroid cancer should be carefully assessed to minimize risk.

For patients with low-risk thyroid cancer, ablation when indicated could be achieved with 1.1 GBq radioactive iodine after recombinant human thyroid-stimulating hormone (rhTSH) injections, as this combination reduces whole body irradiation and maintains quality of life, according to findings published in The Lancet Diabetes/Endocrinology.

The ESTIMABL1 (ClinicalTrials.gov Identifier: NCT00435851) randomized phase 3 trial assessed radioactive iodine treatment following complete surgical resection in 752 patients with low-risk thyroid cancer.

A total of 92% of patients had complete thyroid ablation at 6 to 10 months, which the authors defined as rhTSH- stimulated serum thyroglobulin concentration ≤1 ng/mL and normal findings on sonographic imaging. The results showed equivalence between low-activity (1.1 GBq) and high-activity (3.7 GBq) radioactive iodine, as well as between rhTSH injections and thyroid hormone withdrawal.

Patients were randomly assigned to 1 of 4 strategies, with each combining 1 of 2 methods of thyrotropin stimulation (administration of rhTSH or thyroid hormone withdrawal) and 1 of 2 radioactive iodine activities (1.1 GBq or 3.7 GBq).  Of the original cohort, 726 patients were included in long-term analysis.

At 5-year follow-up, the majority of patients (n=715, 98%) showed no evidence of disease; 4 demonstrated structural disease, 5 had elevated serum thyroglobulin concentration, and 2 showed indeterminate findings on neck ultrasonography. Of this subgroup, 6 individuals received 1.1 GBq radioactive iodine while 5 received 3.7 GBq.

The authors note that an “increasing concentration of postoperative TSH-stimulated serum thyroglobulin at the time of ablation was prognostic for persistent structural disease at the time of ablation, for incomplete ablation status at 6-10 months, and for disease status at last follow-up.”

Thus, undetectable serum thyroglobulin concentrations prior to ablation “is reassuring and might help to avoid use of radioactive iodine in patients with no other risk factors for persistent disease,” they add.

Reference

Schlumberger M, Leboulleux S, Catargi B, et al. Outcome after ablation in patients with low-risk thyroid cancer (ESTIMABL1): 5-year follow-up results of a randomised, phase 3, equivalence trial [published online May 25, 2018].  Lancet. doi: https://doi.org/10.1016/S2213-8587(18)30113-X

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