Differentiated thyroid cancer (DTC) is generally associated with a favorable prognosis. Nevertheless, a clinically important subgroup of patients faces risks of recurrence and disease-specific mortality. Historically, aggressive treatment, including total thyroidectomy and routine adjuvant radioactive iodine (RAI) therapy, was widely applied. This strategy, however, has come under increasing scrutiny for contributing to overtreatment, unnecessary complications, and reduced quality of life in patients with low-risk disease. Accordingly, the 2015 American Thyroid Association (ATA) guidelines emphasized the need for a systematic risk stratification system (RSS), distinct from purely anatomical staging, to guide treatment intensity [1]. An RSS enables a more nuanced and continuous assessment of recurrence risk by incorporating pathological prognostic factors not captured in the American Joint Committee on Cancer/Union for International Cancer Control tumor, node, metastasis (TNM) staging system [1].

Recently, Moon et al. [2] summarized the main updates to the original RSS for DTC presented in the 2024 Korean Thyroid Association (KTA) guideline [3]. The KTA’s risk stratification system (K-RSS), though structurally based on the 2015 ATA modified RSS (M-RSS), integrates refinements grounded in extensive clinical experience and data specific to the Korean population. Four major revisions characterize the K-RSS. First, reclassification was performed in alignment with the 2022 World Health Organization (WHO) classification of tumors [4]. Second, invasive encapsulated follicular variant of papillary thyroid carcinoma (PTC), follicular thyroid carcinoma, and oncocytic thyroid carcinoma, which share recurrence risks and related factors, were consolidated into the category of encapsulated follicular-patterned thyroid carcinoma. Third, the low-risk group was defined as cases with recurrence rates of 5% or less, while the high-risk group was defined as those with recurrence rates of 30% or more, with patients between these thresholds classified as intermediate risk. Finally, for the intermediate-risk group, recurrence prediction is recommended using a combination of multiple clinical factors, including detailed pathological features, primarily informed by Korean studies. This represents a shift from assigning recurrence risk based solely on a single risk factor [2].

The 2025 ATA guideline reflects a decade of accumulated evidence since the 2015 version and introduces several key updates in risk stratification. Most notably, the intermediate-risk group has been subdivided into ‘low-intermediate’ and ‘intermediate-high,’ creating a continuum of recurrence risk rather than a rigid three-tier system. Patients in the low-intermediate group may safely avoid unnecessary RAI therapy or intensive surveillance, while those in the intermediate-high group warrant closer monitoring [5]. Margin status, absent from the 2015 ATA M-RSS, has now been explicitly included. Microscopically positive margins (R1), particularly posterior margins, are classified as low-intermediate risk [5]. The 2025 ATA RSS also provides more specific thresholds for lymph node (LN) metastasis burden and vascular invasion, enabling a more granular recurrence risk assessment. In addition, it incorporates the 2022 WHO histologic classification. While routine postoperative molecular profiling of histologic specimens is not recommended, the guideline recognizes molecular markers such as BRAF^V600E and telomerase reverse transcriptase (TERT) promoter mutations as significant modifiers of risk when identified, particularly when present together. Molecular risk should be considered alongside ATA recurrence categories, postoperative thyroglobulin levels, and imaging results [5].

The 2025 ATA RSS and 2024 K-RSS share core principles but also highlight some distinctions. Both guidelines demonstrate strong philosophical alignment, reflecting a growing international consensus in the management of DTC. Each system emphasizes that recurrence risk is not typically determined by a single factor but rather by the cumulative influence of multiple coexisting factors. A central shared goal is the minimization of overtreatment. Both systems aim to identify, with confidence, a large cohort of low-risk patients who can safely forgo routine RAI therapy and maintain less stringent thyroid-stimulating hormone suppression targets. By doing so, they reduce treatment-related morbidity while improving quality of life.

Both the 2024 K-RSS and the 2025 ATA RSS downweight isolated microscopic extrathyroidal extension (ETE), classifying it as low risk in the K-RSS and low-intermediate in the ATA RSS. Importantly, the 2024 K-RSS distinguishes between the severity of gross ETE by downgrading T3b disease (invasion of strap muscles only) to the intermediate-risk category. In contrast, the 2025 ATA RSS continues to classify T3b as high risk. This adjustment in the K-RSS reflects a contextualized, data-driven refinement that favors treatment de-escalation for T3b, acknowledging its relatively lower recurrence risk in the Korean population. Another difference is that the 2024 K-RSS does not classify multifocality alone as an independent risk factor, whereas the 2025 ATA RSS differentiates between unilateral and bilateral multifocality, incorporating tumor size into risk determination (Table 1). Both systems adopt refined terminology, such as ‘encapsulated follicular-patterned thyroid carcinoma,’ ‘oncocytic thyroid carcinoma,’ and ‘high-grade differentiated thyroid carcinoma,’ based on the 2022 WHO classification, and both require pathology reports to include subtype-specific details. Furthermore, both note that the coexistence of multiple intermediate-risk features cumulatively increases recurrence risk [2,5]. Unlike the 2015 ATA M-RSS, neither the 2024 K-RSS nor the 2025 ATA RSS includes serum thyroglobulin in the high-risk category due to the absence of a standardized cutoff.

The 2025 ATA and 2024 KTA RSS share the overarching goal of personalization but diverge in how they weight specific pathological features. The two systems differ in threshold definitions, categorical rules, and the operationalization of molecular data. While the 2024 K-RSS retains the framework of the 2015 ATA M-RSS, it introduces more precise, data-driven modifications derived from extensive Korean clinical experience and research. Specifically, the 2024 K-RSS explicitly defines risk groups according to estimated 10-year recurrence probabilities: low ≤5%, intermediate >5%–30%, and high >30%. It also applies numeric thresholds for key variables such as tumor size and the number or size of metastatic LNs, while permitting aggregation of multiple intermediate features to upstage patients into the high-risk category [2]. The 2025 ATA RSS, although maintaining categorical divisions, introduces slightly different percentage ranges, subdividing intermediate cases into low-intermediate and intermediate-high groups [4]. Regarding vascular invasion, the 2024 K-RSS applies explicit numeric thresholds across follicular-patterned tumors (≤3 foci=intermediate; ≥4 foci=high) and extends these cutoffs to PTC. This granular vascular invasion rule is one of the notable innovations of the K-RSS. By contrast, the 2025 ATA RSS does not specify numeric cutoffs but generally categorizes vascular invasion in PTC as intermediate-high risk. Another distinction is molecular re-stratification: the 2024 K-RSS incorporates explicit molecular findings, considering PTCs 1 to 2 cm with BRAF^V600E mutations to be lower risk than in prior Korean schemas, while defining the presence of two or more high-risk mutations (e.g., BRAF^V600E+TERT promoter, or RAS+TERT) as a criterion for high risk. Table 1 summarizes these comparisons between the 2024 K-RSS and the 2025 ATA RSS.

Together, the 2025 ATA and 2024 KTA guidelines represent significant advances in thyroid cancer risk stratification, marking a transition from broad classification toward genuine personalization. Postoperative initial risk assessment now integrates coexisting clinical and pathological factors comprehensively, moving beyond reliance on any single risk element. Although some distinctions remain between the two systems, these updates collectively bring the field closer to precision oncology.

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References

• 1. Haugen BR, Alexander EK, Bible KC, Doherty GM, Mandel SJ, Nikiforov YE, et al. 2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer: the American Thyroid Association guidelines task force on thyroid nodules and differentiated thyroid cancer. Thyroid 2016;26:1–133.PubMedPMC
• 2. Moon S, Song YS, Jung KY, Lee EK, Lee J, Lim DJ, et al. The initial risk stratification system for differentiated thyroid cancer: key updates in the 2024 Korean Thyroid Association guideline. Endocrinol Metab (Seoul) 2025;40:357–84.ArticlePubMedPMCPDF
• 3. Lee EK, Song YS, Kang HC, Kim SW, Na DG, Moon SJ, et al. Korean Thyroid Association guidelines on the management of differentiated thyroid cancers. Part I. Initial management of differentiated thyroid cancers. Chapter 5. Evaluation of recurrence risk postoperatively and initial risk stratification in differentiated thyroid cancer 2024. Int J Thyroidol 2024;17:68–96.Article
• 4. Baloch ZW, Asa SL, Barletta JA, Ghossein RA, Juhlin CC, Jung CK, et al. Overview of the 2022 WHO classification of thyroid neoplasms. Endocr Pathol 2022;33:27–63.ArticlePubMedPDF
• 5. Ringel MD, Sosa JA, Baloch Z, Bischoff L, Bloom G, Brent GA, et al. 2025 American Thyroid Association management guidelines for adult patients with differentiated thyroid cancer. Thyroid 2025;35:841–985.ArticlePubMedPMCPDF

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