Radioactive iodine ablation may not decrease the risk of recurrence in intermediate-risk papillary thyroid carcinoma

The use of radioactive iodine (RAI) ablation in patients with intermediate-risk papillary thyroid carcinoma (PTC) who show microscopic extrathyroidal extension (ETE), regional lymph node (LN) metastasis, tumors with aggressive histology, or vascular invasion has been debated due to the lack of data regarding long-term prognosis in this risk group. Therefore, the purpose of this study was to resolve the controversy surrounding the prognostic benefit of RAI ablation, especially in intermediate-risk PTC patients. We retrospectively reviewed the medical records of 8297 intermediate-risk PTC patients who underwent primary total thyroidectomy with or without neck dissection at the Thyroid Cancer Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea, between January 1997 and June 2015. Of these 8297 patients, 7483 (90.2%) received RAI ablation. After adjusting for clinicopathological characteristics, RAI ablation did not significantly decrease the risk of loco-regional recurrence (LRR) (adjusted hazard ratio (HR) = 0.852, P = 0.413). Moreover, RAI ablation did not decrease the risk of LRR even in intermediate-risk PTC patients with aggressive features such as BRAF positivity (adjusted HR = 0.729, P = 0.137), tumor size >1 cm (adjusted HR = 0.762, P = 0.228), multifocality (adjusted HR = 1.032, P = 0.926), ETE (adjusted HR = 0.870, P = 0.541), and regional LN metastasis (adjusted HR = 0.804, P = 0.349). Furthermore, high-dose RAI ablation (>100 mCi) did not significantly decrease the risk of LRR (adjusted HR = 0.942, P = 0.843). Therefore, RAI ablation in intermediate-risk PTC patients should be considered on the basis of tailored risk restratification.