Long-Term Outcomes Following Low-Dose Radioiodide Ablation for Differentiated Thyroid Cancer

Abstract

Randomized trials show that low-dose (1.1 GBq [30 mCi]) radioiodide (RAI) has efficacy equivalent to high-dose RAI (3.7 GBq [100 mCi]) in thyroid remnant ablation (TRA) for differentiated thyroid cancer. Long-term follow-up is required to ensure detection of late recurrences and to confirm equivalence in terms of survival end points. However, median follow-up duration within randomized trials is currently limited. We studied 53 patients undergoing TRA for differentiated thyroid cancer with long-term follow-up in the Thyroid Unit of The Royal Marsden Hospital (Sutton, United Kingdom). Patients were treated with TRA using low-dose (1.1 GBq) RAI. Disease-free survival, overall survival, and the incidence of second malignancies were measured. Multivariable analysis was used to determine clinical risk factors for failure to achieve TRA after low-dose RAI. Median follow-up was 24 (range, 4-34) years. Low-dose RAI TRA was successful in 26 (49%) patients (successful ablation [SA] group), whereas 27 (51%) patients required further treatment (unsuccessful ablation [UA] group). Thirty-year disease-free survival was 92% in the SA group vs 87% in the UA group (P = .601). Thirty-year overall survival was 81% in the SA group vs 62% in the UA group (P = .154). Nine (17%) patients developed second malignancies (4 in the SA group and 5 in the UA group). Predictors of failure to achieve TRA with low-dose RAI were male sex and stage pT4 disease. There is no evidence from long-term follow-up of our cohort that treatment outcomes are compromised for patients that fail TRA with low-dose RAI and subsequently receive high-dose RAI.