Low-Dose Radioiodine Effective in Low-Risk Thyroid Cancer
Between 1973 and 2002, the incidence of thyroid cancer has nearly tripled in the US, from 2.7 to 7.7 cases per 100,000, with similar increases reported in Europe. “Such increases appear to result largely from more frequent radiologic detection and subsequent fine-needle aspiration of small thyroid nodules, leading to the diagnosis of low-risk thyroid cancer,” an accompanying editorial noted.
In the first study, a Phase 3 trial conducted in France, 752 patients who had undergone total thyroidectomy for differentiated thyroid carcinoma (92% papillary cancer) were randomized between 2007 and 2010 to one of two thyrotropin-stimulation methods: thyroid hormone withdrawal and use of recombinant human thyrotropin, and two radioiodine (131I) doses: 1.1GBq and 3.7GBq, in a 2-by-2 design.
Eight months after administration of radioiodine, the investigators assessed thyroid ablation by neck ultrasonography and measurement of recombinant human thyrotropin–stimulated thyroglobulin.
In 684 evaluable patients, ultrasonography of the neck was normal in 652 (95%). Stimulated thyroglobulin level was ≤1.0ng/mL in 621 of the 652 patients (95%) without detectable thyroglobulin antibodies. Thyroid ablation was complete in 631 patients (92%), and the rate was equivalent between the 131I doses and between the thyrotropin stimulation methods, with no unexpected serious adverse events, they found.
The second study, a randomized noninferiority trial conducted in the United Kingdom, compared low-dose and high-dose radioiodine, each in combination with either thyrotropin alfa or thyroid hormone withdrawal before ablation. Patients had tumor stage T1 to T3, with possible spread to nearby lymph nodes but without metastasis.
Of 438 patients who underwent randomization, 421 were evaluable. “Ablation success rates were 85.0% in the group receiving low-dose radioiodine vs. 88.9% in the group receiving the high dose and 87.1% in the thyrotropin alfa group versus 86.7% in the group undergoing thyroid hormone withdrawal,” they wrote, and the differences indicated noninferiority. “Similar results were found for low-dose radioiodine plus thyrotropin alfa (84.3%) vs. high-dose radioiodine plus thyroid hormone withdrawal (87.6%) or high-dose radioiodine plus thyrotropin alfa (90.2%).”
More patients in the high-dose group (36.3%) than in the low-dose group (13.0%) were hospitalized for at least 3 days (P<0.001). Adverse events occurred in 21% of the low-dose group and 33% in the high-dose group (P=0.007); 23% in the thyrotropin alfa group vs. 30% in the group undergoing thyroid hormone withdrawal reported adverse events (P=0.11).