Clinical Significance of Tumor Size in Gross Extrathyroidal Extension to Strap Muscles (T3b) in Papillary Thyroid Carcinoma: Comparison with T2

SIMPLE SUMMARY: In the 8th edition of the AJCC/UICC TNM staging system, T3b is defined as gross extrathyroidal extension (gETE) invading only the strap muscles from a tumor of any size. However, defining T3b according to tumor size remains controversial. We created new T3b categories according to tumor size (T3b-1, tumor ≤ 2 cm in T3b; T3b-2, 2 cm < tumor ≤ 4 cm in T3b). There was a significant difference only in T3b-2 compared to T2. Novel methods of evaluating the effect of gETE according to tumor size should be considered in further revisions of the AJCC/UICC TNM staging system. ABSTRACT: The purpose of the present study was to compare the risk of recurrence between T2 and T3b papillary thyroid carcinoma (PTC) and the effect of tumor size on survival in T3b disease. A total of 634 patients with PTC who underwent thyroid surgery at a single center were retrospectively analyzed. Clinicopathological characteristics were compared according to the T category in the TNM staging system, with T3b divided into T3b-1 (tumor size, ≤2 cm) and T3b-2 (tumor size, 2–4 cm). Disease-free survival (DFS) and recurrence risk were compared between T2, T3b, T3b-1, and T3b-2. Tumor size was significantly larger in T2 than in T3b. A significant difference in recurrence was observed between T2 and T3b-2 but not between T2 and T3b-1. T3b-2 was identified as a significant risk factor for PTC recurrence. A significant difference in the DFS curve was observed between T2 and T3b-2. However, no significant differences in survival were observed between T2 and T3b or T3b-1. These results indicate that the prognostic impact of T3b may vary depending on tumor size. Further studies are required to determine the need for T classifications that account for tumor size and gETE invasion of the strap muscles.