The phase 3 ESTIMABL2 trial has revealed groundbreaking evidence that challenges traditional post-thyroidectomy treatment protocols for low-risk differentiated thyroid cancer. The five-year analysis, published in The Lancet Diabetes and Endocrinology, demonstrates that omitting radioiodine (131I) administration after surgery produces comparable outcomes to standard radioiodine treatment.
Key Trial Outcomes
The study, which followed 698 patients, reported remarkable event-free survival (EFS) rates at five years: 94.8% (95% CI, 91.9%-96.7%) in the radioiodine group (n=344) compared to 93.2% (95% CI, 90.1%-95.4%) in the no-radioiodine group (n=354). The difference between groups was -1.6% (90% CI, -4.5% to 1.4%), falling well within the predetermined noninferiority margin of -5%.
Dr. Sophie Leboulleux, lead investigator from Institut Gustave Roussy, emphasized the significance of these findings: "There is no loss of opportunity in following these patients without postoperative ablation." This statement underscores the potential paradigm shift in thyroid cancer management.
Treatment Response and Patient Characteristics
Notably, the study revealed superior outcomes in certain aspects for patients who did not receive radioiodine. According to the 2015 American Thyroid Association treatment response criteria, 83.3% of patients in the no-radioiodine group achieved an excellent response, compared to 75.6% in the radioiodine group. The radioiodine group showed a higher rate of indeterminate responses (19.8% vs 7.3%).
The trial included a well-balanced patient population across both arms. The median age was approximately 52 years, with over 80% female participants. Most patients (>95%) had papillary histology, with median tumor sizes of 13-14mm.
Trial Design and Methodology
The ESTIMABL2 trial (NCT01837745) randomly assigned 776 patients with low-risk differentiated thyroid cancer to either receive postoperative radioiodine (n=389) or follow a non-radioiodine strategy (n=387). Patients in the radioiodine group received 1.1 GBq of radioiodine under carefully controlled conditions, including thyrotropin stimulation.
Follow-up Protocol
The study implemented a comprehensive follow-up strategy for both groups. Initial assessment included thyroglobulin measurement under recombinant human-thyrotropin-stimulating hormone stimulation, thyroglobulin antibody measurement, and neck ultrasonography at 10 months post-randomization. Subsequent monitoring involved annual thyroglobulin measurements and biennial neck ultrasonography.
Clinical Implications
These findings have significant implications for thyroid cancer treatment, suggesting that carefully selected low-risk patients might safely avoid radioiodine treatment after thyroidectomy. This could potentially reduce treatment burden, healthcare costs, and radiation exposure while maintaining excellent oncological outcomes.
