Endocrine Abstracts

Background: To minimize potential harm from overtreatment of low-risk thyroid cancers, the 2015 American Thyroid Association (ATA) Guidelines recommend that radioactive iodine (RAI) ablation should not be routinely used in low-risk differentiated thyroid carcinoma (DTC). The present study aims to evaluate trends in RAI therapy in a tertiary center after the update of these Guidelines.

Methods: Data from patients followed in a tertiary center with low-risk DTC between 2016 e 2019 were analyzed. Risk stratification was based on 2015 ATA stating criteria. Multifocality, minimal extrathyroidal extension, ≤5 pathologic N1 micro-metastases (<0.2 cm in largest dimension), non-specific findings or suspicious lymph nodes on post-operative ultrasound (US), non-stimulated serum thyroglobulin (Tg) >1 ng/ml and positive anti-Tg were considered potential risk factors for recurrence.

Results: A total of 739 low-risk DTC patients were included (77.9% female) with a mean age of 53.7±15.9 years-old. All patients underwent RAI therapy after recombinant human TSH. The number of RAI therapies in low-risk DTC reduced from 53.9% (2016) to 27.8% (2019). All risk factors for recurrence were significant for RAI ablation decision: multifocality (59.5%; P<0.001); non-specific findings on post-op US (35.6%; P<0.001); minimal extrathyroidal extension (23.1%; P<0.001); non-stimulated serum Tg >1 ng/ml (20.8%;P=0.002); suspicious lymph nodes on post-op US (11.5%; P<0.001); N1 micro-metastases (5.1%; P<0.001) and positive anti-Tg (4.8%;P=0.008). RAI activity on overall years was 52.7±32.0 mCi and a decrease was observed between 2016 and 2109 (52.8±31.4 to 40.6±24.1 mCi). Higher activities of RAI were observed in patients with N1 micro-metastases (P=0.004) and extrathyroidal extension (P=0.054).

Conclsions: Our data demonstrates that the number of RAI treatments of low-risk DTC decreased substantially since the update of ATA recommendations. All considered risk factors were significant for RAI treatment decision. The presence of micro-metastases and extrathyroidal extension were associated with higher activities of RAI.