Prognostic significance of minimal extrathyroidal extension in differentiated thyroid carcinoma: a retrospective cohort study

Abstract

Objectives: To evaluate the impact of minimal Extrathyroidal Extension (mETE) on structural recurrence, prognostic variables, and disease-free survival in patients with Differentiated Thyroid Carcinoma (DTC) treated surgically. Methods: A retrospective cohort of 629 patients who underwent thyroidectomy for DTC was analyzed. Patients were divided into two groups: Group 1 (n = 413) with tumors confined to the thyroid, and Group 2 (n = 216) with minimal extrathyroidal extension. Clinical, pathological, and biochemical variables were compared between groups. The minimum follow-up period was 30-months or until death, with an average follow-up of 71.5-months. Univariate and multivariate analyses were performed to identify independent predictors of structural recurrence. Results: Structural recurrence occurred in 6.5% of Group 1 and 22.7% of Group 2 patients (p < 0.001). Group 2 showed significantly higher rates of follicular carcinoma, tumor size > 2 cm, angiolymphatic invasion, pN1 disease, multicentricity, elevated postoperative thyroglobulin (Tg > 10 ng/mL), iodine-refractory disease, distant metastases, and higher late Tg levels (all p < 0.05). Even though the univariate associations were statistically significant, multivariate analysis identified only male sex (p = 0.018), postoperative Tg >10 ng/mL (p < 0.001), and iodine-refractory disease (p < 0.001) as independent predictors of structural recurrence, not mETE. Five-year disease-free survival was 94.1% in Group 1 and 79.2% in Group 2 (p < 0.001). Conclusion: Minimal extrathyroidal extension was associated with several adverse prognostic factors and worse outcomes in univariate analysis. However, it was not an independent predictor of structural recurrence or reduced disease-free survival in this cohort. These findings highlight the need to understand mETE in the larger context of risk stratification in management of DTC. Level of evidence: 3.