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Low-dose, high-dose radioiodine ablation equivalent in differentiated thyroid cancer

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International Thyroid Congress

PARIS — Low-dose radioiodine ablation appears to be as effective as standard high-dose radioiodine ablation, with or without recombinant human thyroid-stimulating hormone, for eradication of thyroid remnants in patients who underwent thyroidectomy for differentiated thyroid cancer, according to preliminary phase 3 data presented here at the International Thyroid Congress.

Two randomized, controlled, multicenter studies compared four strategies of postoperative radioiodine ablation. Each strategy combined a TSH stimulation method of recombinant hormone TSH (rhTSH) or thyroid hormone withdrawal and a radioiodine ablation method of low-dose 1.1 GBq (30 mCi) or higher-dose 3.7 GBq (100 mCi).

Results of both studies demonstrated a similar effect of the strategies.

“This is a major revert, showing equivalence between these four strategies,” Bogdan Catargi, MD, of the University Hospital of Bordeaux, France, said during his presentation of the ESTIMABL data.

Researchers for the ESTIMABL study randomly assigned 753 patients with differentiated thyroid cancer who underwent total thyroidectomy for differentiated papillary or follicular thyroid carcinoma to the four different strategies. Neck ultrasound and rhTSH-stimulated thyroglobulin determination were used to assess thyroid ablation at 6 and 10 months after radioiodine ablation.

Initial follow-up revealed that the ablation success rate was 89% in the two groups assigned rhTSH (Thyrogen, Genzyme) and low- and high-dose radioiodine ablation. In the thyroid hormone withdrawal groups, 92% of patients treated with 1.1 GBq had a complete ablation success rate compared with 93% of patients assigned to 3.7 GBq.

“This study suggests equivalence in ablation rate at 8 months,” Catargi said. “If confirmed by the final analysis, this will validate the use of rhTSH and 1.1 GBq for ablation in low-risk patients.”

Ujjal K. Mallick, MD, of Freeman Hospital in Newcastle-upon-Tyne, U.K., presented preliminary data from the HiLo study, which included 438 patients who were randomly assigned to the four strategies besides a low-iodine diet. A radioiodine diagnostic scan was used to determine ablation success 6 to 9 months later.

Ablation success rates ranged from 93% to 95% with the four strategies, based on data from 258 patients who completed 9 months of follow-up. No differences were present in subgroup analyses or when the researchers examined tumor stage and nodal involvement.

“Comparison of the four groups showed hardly any difference,” Mallick said.

In addition, quality-of-life data from the HiLo study showed that low-dose 1.1 GBq radioiodine ablation was associated with shorter hospital stays and fewer days missed from work compared with the 3.7-GBq dose.

Catargi and Mallick said these data are preliminary, and results are pending for other patients in both studies. – by Katie Kalvaitis

For more information:

• Catargi B. OC-067.

• Mallick U. OC-068. Both presented at: the 14th International Thyroid Congress; Sept. 11-16, 2010; Paris.

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