Impact of Tumor Size on Prognosis in Differentiated Thyroid Cancer with Gross Extrathyroidal Extension to Strap Muscles: Redefining T3b.

Simple Summary: This study investigated the impact of tumor size on T3b differentiated thyroid cancer prognosis. No significant difference was found in the prognosis of small T3b tumors compared to the T1 tumors. Disease-specific survival, disease-free survival, and overall survival were significantly lower only in large T3b tumors compared to T2 and T3a. If T3b tumors are 2 cm or smaller, downstaging may be considered. The modified T category, reclassifying T3b (≤2 cm) as T1, showed better staging performance than the existing category. Adopting this modified T category could improve the prognostic accuracy of the AJCC/TNM staging. The prognostic significance of tumor size in T3b differentiated thyroid cancer (DTC) remains debated and underexplored. This study aimed to examine the varying impact of T3b based on tumor size, analyzing disease-specific survival, disease-free survival, and overall survival. A retrospective review of 6282 DTC patients who underwent thyroid surgery at Seoul St. Mary's Hospital from September 2000 to December 2017 was conducted. T3b was classified into three subcategories, T3b-1 (≤2 cm), T3b-2 (2–4 cm), and T3b-3 (>4 cm), using the same size criteria for T1, T2, and T3a. T3b-1 showed no significant difference in disease specific survival compared to T1, and both disease-free and disease-specific survival curves were sequentially ranked as T1, T3b-1, T2, T3a, T3b-2, and T3b-3. The modified T category, reclassifying T3b-1 as T1, demonstrated superior staging performance compared to the classic T category (c-index: 0.8961 vs. 0.8959 and AUC: 0.8573 vs. 0.8518). Tumors measuring 2 cm or less within the T3b category may require downstaging, and a modified T category could improve the precision of prognostic staging compared to the current T category. [ABSTRACT FROM AUTHOR]