Low-Dose Radioiodine Ablation Is Effective Treatment for Thyroid Cancer

Low-dose radioiodine ablation with thyrotropin alfa is as effective as high-dose radioiodine ablation in patients with differentiated thyroid cancer and is safer, researchers reported.

The results also show that the efficacy of low-dose radioiodine ablation is maintained when thyrotropin alfa is used instead of thyroid hormone withdrawal. Ujjal Mallick, MD, consultant clinical oncologist at the Northern Centre for Cancer Treatment in Newcastle upon Tyne, England, and colleagues randomized 438 patients to one of four treatment groups: low-dose (1.1 GBq) or high-dose (3.7 GBq) radioiodine, each combined with thyrotropin alfa or thyroid hormone withdrawal.

Thyroid cancer is the most common endocrine cancer, and more than 48,000 new cases are reported annually in the United States, the authors noted. The incidence of thyroid cancer is increasing worldwide and more than doubled in the United States from 1973 through 2006.

There are multiple advantages to using a lower dose of radioiodine, including shorter time in hospital isolation and fewer side effects, including a second primary cancer due to exposure to radioactive substances, they added. Ultimately, financial costs are also reduced.

Study participants had tumor stage T1 to T3 with the possibility of lymph node involvement but no distant metastasis.

The primary endpoint was the success rate for ablation, which was defined as both a negative scan on whole-body iodine-131 scanning (<0.1% uptake on the basis of the region-of-interest method drawn over the thyroid bed) and a thyroglobulin level of less than 2.0 ng/mL at 6 to 9 months.

Results showed that ablation was successful in 85.0% of patients randomized to low-dose radioiodine versus 88.9% of patients assigned to high-dose radioiodine. Ablation success rates were 87.1% in the thyrotropin alfa group and 86.7% in the group undergoing thyroid hormone withdrawal.

Similar results were documented for low-dose radioiodine plus thyrotropin alfa (84.3%) versus high-dose radioiodine plus thyroid hormone withdrawal (87.6%) or high-dose radioiodine plus thyrotropin alfa (90.2%).

The study also found that ablation rates were similar for low- and high-dose radioiodine ablation with either thyrotropin alfa or thyroid hormone withdrawal in subgroups of patients with T3 stage tumors and lymph node involvement.

Overall, 36.3% of patients in the high-dose group were hospitalized for at least 3 days versus 13.0% of patients in the low-dose group (P <.001). Also, 33% of patients in the high-dose group had adverse events versus 21% of patents in the low-risk group (P = .007) and 23% of patients in the thyrotropin alfa group versus 30% of patients in the group undergoing thyroid hormone withdrawal (P = .11).

“Our study answers two central questions involving radioiodine ablation of thyroid remnants after surgery for differentiated thyroid cancer; namely, that the efficacy of low-dose radioiodine is similar to that of high-dose radioiodine, and that the efficacy of lowdose radioiodine ablation is not compromised by the use of thyrotropin alfa instead of thyroid hormone withdrawal,” Mallick and colleagues wrote. “Previous small studies had conflicting results on both counts.”

They emphasized that their study focused on ablation success at 6 to 9 months and does not provide information on future recurrences.

Mallick U, Harmer C, Yap B, et al. Ablation with low-dose radioiodine and thyrotropin alfa in thyroid cancer. N Engl J Med. 2012;366(18):1674-1685.