Schlumberger M, et al. - Researchers sought to report the outcomes after 5 years of follow-up following ablation in patients with low-risk thyroid cancer (ESTIMABL1). ESTIMABL1 was a randomized phase 3 trial in which radioactive iodine (¹³¹I) was administered following complete surgical resection in patients with low-risk thyroid cancer. Previously, complete thyroid ablation was achieved in 92% of patients at 6–10 months. Low-activity (1.1 GBq) and high-activity (3.7 GBq) radioactive iodine, as well as the use of recombinant human thyroid-stimulating hormone (rhTSH) injections and thyroid hormone withdrawal were shown to be equivalent. In the present work, they observed no correlation of disease recurrence with the approach used for ablation. Data thereby support using 1.1 GBq radioactive iodine after rhTSH for postoperative ablation in patients with low-risk thyroid cancer.

Methods

• At 24 centers in France, researchers performed a multicenter, randomized, open-label, equivalence trial.
• Between March 28, 2007 and February 25, 2010, adults with low-risk differentiated thyroid carcinoma who had undergone total thyroidectomy were randomized (1:1:1:1) to one of four strategies, each combining one of two methods of thyrotropin stimulation (rhTSH or thyroid hormone withdrawal) and one of two radioactive iodine activities (1.1 GBq or 3.7 Gbq).
• Computer-generated sequence was used to perform randomization with variable block size.
• Yearly serum thyroglobulin measurement on levothyroxine treatment comprised the follow-up.
• As per physician discretion, measurement of rhTSH-stimulated thyroglobulin and neck ultrasonography were done.
• Presence of serum thyroglobulin of 1 ng/mL or less on levothyroxine treatment and normal results on neck ultrasonography constituted the definition of no evidence of disease.

Results

• Researchers performed follow-up on 726 patients (97% of the 752 patients originally randomized).
• No evidence of disease was observed in 715 (98%) at a median follow-up of 5.4 years since randomization (range 0.5–9.2).
• Structural disease (n=4), raised serum thyroglobulin concentration (n=5), or indeterminate findings on neck ultrasonography (n=2) was reported in remaining 11 patients; of these, 6 received 1.1 GBq radioactive iodine (five after rhTSH and one after withdrawal) and 5 received 3.7 GBq (two after rhTSH and three after withdrawal) at ablation.
• Estimates of TSH-stimulated (either after rhTSH injections or thyroid hormone withdrawal according to the treatment group) thyroglobulin concentration at the time of ablation was predictive of structural disease status at ablation, ablation status at 6–10 months, and the final outcome.