Timing of radioactive iodine administration does not influence outcomes in patients with differentiated thyroid carcinoma: Beyond the Abstract

In this study, we demonstrated that the time between total thyroidectomyt (TT) and RAI administration is not the primary determinant of DTC outcome, at least if administered within the first year after TT. This finding was consistent across all categories of TNM stage and ATA risk stratification.

Methods and Main Results

From a cohort of 901 patients who were consecutively attended in the Thyroid Outpatient Clinic of the Endocrine Division of Hospital de Clínicas de Porto Alegre (HCPA), a tertiary care university teaching hospital in southern Brazil, we selected 545 individuals with a histological diagnosis of DTC who received RAI therapy.

The median time interval between TT and RAI was 6 months (P25-75, 3-10). To investigate whether the timing of RAI administration impact on the response to the initial treatment, the patients were assigned to two groups according to the time interval between TT and RAI: less than 6 months after TT (Group A, n=295) or more than 6 months (group B, n=250). The median time interval in Group A was 3 months (P25-75 2-5) and in group B it was 10.5 months (P25-75, 8-16). 

One year after the initial therapy, 59.3% (n = 175) of patients in Group A and 65.6% (n = 164) in Group B were considered disease free (P = 0.15). These findings did not change after a median of 6 years of follow-up (63.3% of the patients were disease free in group A vs. 67.7% in group B, P = 0.31). Next, we looked for the impact of the time interval between TT and RAI administration on the recurrence rates. There were no differences in the recurrence rates between the groups (5.4 vs. 3.0% for group A and B, respectively, P=0.39). The lack of impact of RAI timing was observed across all ATA risk classification categories, including patients classified as high risk (macroscopic tumor invasion or incomplete tumor resection or presence of distant metastases). Remarkably, in those patients, the rate of individuals considered as disease free after initial therapy was 9.5% and 10.0% in group A and B, respectively (P = 1.00) . Similar results were observed after a median of 6 years follow-up.

Clinical Implications

We believe that our findings have important clinical implications. First, we can reassure the patients that the RAI therapy, whenever indicated, can be safely administered at any time within the first year after thyroid surgery. Secondly, the recommendation to RAI treatment can be postponed and re-examined without any harm to the patients, which might be helpful in cases which the role of RAI therapy is not evident, such as in intermediate risk patients. 

Take-home message

The take-home message of the study is that time between the TT and RAI does not affect disease outcomes (response to initial therapy, disease status on follow-up and recurrence rate) in patients with DTC. 

Written by: Rafael Selbach Scheffel