Impact of Minimal Extrathyroid Extension in Differentiated Thyroid Cancer: Systematic Review and Meta-Analysis

Abstract Background Minimal extrathyroid extension (mETE) in patients with differentiated thyroid cancer (DTC) was defined as an intermediate risk feature in the 2015 American Thyroid Association guidelines. However, controversy persists as several studies suggested mETE has little effect on disease outcome. Objective To assess the impact of mETE on DTC patients' outcome. Methods Meta-analysis of controlled trials comparing patients with DTC with and without mETE. Data Extraction and Synthesis Thirteen retrospective studies including 23,816 patients were included, with a median follow-up of 86 months. mETE in patients without lymph node involvement (N0 disease) was associated with increased risk of recurrence [seven studies: odds ratio (OR), 1.73; 95% confidence interval (CI), 1.03 to 2.92]. The absolute risk of recurrence was 2.2% in patients without extension and 3.5% in patients with mETE (P = 0.04). In studies including patients with and without lymph node involvement (N1/N0 disease), mETE resulted in a significantly higher risk of recurrence (eight studies: OR, 1.82; 95% CI, 1.14 to 2.91). The absolute risk of recurrence was 6.2% in patients without extension and 7% in patients with mETE (P = 0.01). In patients with micropapillary carcinoma (