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Low-dose radioiodine sufficient for patients with thyroid cancer
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Lower doses of radioactive iodine removed leftover cancer cells as effectively as higher doses in patients with thyroid cancer, two studies found.
The lower doses also were associated with fewer adverse events.
Ninety percent to 95% of thyroid cancers are classified as differentiated thyroid cancers. Most patients with differentiated thyroid cancer undergo radioactive ablation to remove residual thyroid tissue after surgery.
Radioactive iodine has been associated with increased risk of adverse events, including leukemia, according to background information in one of the two studies.
In the first study, Ujjal Mallick, FRCR, a clinical oncologist at Freeman Hospital Northern Centre for Cancer Care in Newcastle upon Tyne, England, and colleagues conducted a randomized trial that compared low- and high-dose radioiodine combined with thyrotropin alpha (Thyrogen, Genzyme) or thyroid hormone withdrawal before ablation.
Mallick and researchers analyzed 421 patients who were treated at 29 centers in the United Kingdom. All patients had stage I to III tumors that had the potential to spread to lymph nodes.
Ablation proved successful in 182 of 214 patients (85%) in the low-dose group vs. 184 of 207 patients (88.9%) in the high-dose group.
Success rates for low-dose radioiodine plus thyrotropin alpha (84.3%) vs. high-dose radioiodine plus thyrotropin alpha (90.2%) and thyroid hormone withdrawal (87.6%) were consistent as well, according to study results.
More patients in the high-dose group (36.3%) were hospitalized for at least 3 days due to adverse events vs. the low-dose group (13%; P=.001). Rates of adverse events also were lower in the low-dose group (21% vs. 33%).
In the second study — a randomized, open-label, phase 3 study — researchers compared the rate of ablation with low-dose iodine (1.1 gigabecquerel [GBq]) vs. higher doses (3.7 GBq).
Researchers analyzed data from 684 patients aged at least 18 years with low-risk differentiated thyroid cancer. The patients were treated at 24 centers in France from April 2007 to February 2010.
Researchers randomly assigned patients to one of four strategies — combining either recombinant human thyrotropin or thyroid hormone withdrawal with either 1.1 GBq or 3.7 GBq of radioiodine.
The study results show “similar rates of thyroid remnant ablation among patients with thyroid cancer, without evidence of residual disease after surgery when either 1.1 GBq or 3.7 GBq of radioiodine is used and when the patient is prepared by means of either recombinant human thyrotropin or withholding of thyroid hormone,” Martin Schlumberger, MD, professor of oncology in the department of nuclear medicine and endocrine oncology at the University of Paris-Sud, and colleagues wrote in the study.
The complete ablation rate was 91.7% among patients in the recombinant human thyrotropin group vs. 92.9% among patients in the thyroid hormone withdrawal group.
“The use of recombinant human thyrotropin and a low dose … for postoperative radioiodine ablation represents an effective and attractive option for the management of low-risk thyroid cancer that reduces the amount of whole-body irradiation and maintains quality of life,” Schlumberger and colleagues wrote.
For more information:
- Mallick U. N Engl J Med. 2012:366;1674-1685.
- Schlumberger M. N Engl J Med. 2012;366:1663-1673.
Disclosure: Dr. Mallick reports receiving board membership fees from AstraZeneca, as well as board membership, consulting and lecture fees from Genzyme. Dr. Schlumberger reports receiving lecture fees from Genzyme.