The Initial Risk Stratification System for Differentiated Thyroid Cancer: Key Updates in the 2024 Korean Thyroid Association Guideline

In 2024, the Korean Thyroid Association (KTA) introduced a revised Risk Stratification System (K-RSS) for differentiated thyroid cancer, building upon the modified RSS (M-RSS) proposed by the American Thyroid Association in 2015. The K-RSS emphasizes the cumulative impact of coexisting clinical and pathological features, acknowledging that multiple intermediate-risk factors collectively indicate a higher recurrence risk. Histologic classification follows the 2022 World Health Organization classification, consolidating encapsulated follicular-patterned thyroid carcinomas, including invasive encapsulated follicular variant papillary thyroid carcinoma, follicular thyroid carcinoma, and oncocytic carcinoma of the thyroid gland, and stratifying them by the extent of capsular and vascular invasion. High-grade thyroid carcinoma is newly included. Updated criteria for tumor size and extrathyroidal extension (ETE) represent another significant change. BRAFV600E-mutated papillary thyroid carcinomas measuring 1 to 2 cm are now considered lower risk than previously classified in the M-RSS, while encapsulated follicular-patterned tumors larger than 4 cm are considered higher risk. Both minimal ETE and gross ETE confined to the strap muscles have been downgraded to low and intermediate risk, respectively. These changes are accompanied by updates regarding molecular profiling and surgical margin status. Collectively, these updates aim to minimize overtreatment in low-risk patients, while ensuring intensified management for those at higher risk.