Endocrine Abstracts

Introduction: The update of 2015 American Thyroid Association (ATA) guidelines recommend that radioactive iodine (RAI) ablation therapy should be used in line with patients’ risk stratification. However, there is no consensus on benefits of post-operative RAI ablation in patients with low risk differentiated thyroid cancer (DTC). The aim of this study is to compare the outcomes of patients with low risk DCT submitted to RAI ablation with those who were not.

Methods: This is a retrospective study of patients with low risk DTC followed in a tertiary cancer centre between 2016-2019. Clinicopathological features were collected. Clinical outcomes of patients submitted to RAI ablation were compared to a group control. The risk factors considered for recurrence were: multifocality, minimal extrathyroidal extension (ETE), N1 micrometastases (≤5 nodes with <0.2 cm in largest dimension), suspicious or non-specific findings on post-operative ultrasound (US), positive non-stimulated serum thyroglobulin (Tg) and positive Tg antibodies (ATG) levels. Remission was defined as no evidence of disease /indeterminate response and disease recurrence as biochemical or structural evidence of disease, at last follow-up, based on ATA criteria.

Results: 739 patients were included (77.9% female) with a mean age of 53.7±15.9 years-old and a mean follow-up of 3.6±1.2 years. RAI ablation was performed in 45%(n=331). Recurrence was observed in 4.2% (n=14) of the patients submitted to RAI ablation and in 2.9% (n=12) of the cases that underwent surveillance (P=0.342). Multivariate analysis showed that only post-op Tg - Tg>1 ng/ml [P<0.001; hazard ratio (HR): 9.5; 95% confidence interval (95%CI):3.0-30.0), Tg between 0.2-1 ng/ml (P=0.008;HR: 5.3; 95%CI: 1.6-18.1)- and suspicious findings on post-op US (P<0.001;HR: 8.7; 95%CI: 2.8-27.8) were independent risk factors for recurrence.

Conclusions: Our results demonstrated no differences in clinical outcomes between RAI ablation and surveillance after surgery in low-risk DTC patients, reinforcing that these patients do not benefit from RAI ablation. Positive non-stimulated serum Tg levels and suspicious findings on post-operative ultrasound were the only factors associated with recurrence.