Background: Minimal extra-thyroid extension (mETE) in differentiated thyroid cancer (DTC) patients 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 DTC patients 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 (7 studies, OR 1.73, 95%CI 1.03-2.92). 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 (8 studies, OR 1.82, 95%CI 1.14-2.91). The absolute risk of recurrence was 6.2% in patients without extension and 7% in patients with mETE (p=0.01). In patients with micro-papillary carcinoma (<1cm) the impact of mETE was non-significant (OR 2.40, 95%CI 0.95-6.03). Minimal ETE had no impact on disease-related mortality (8 studies, OR 0.5, 95%CI 0.11-2.21).
Conclusion: mETE increases risk of recurrence in DTC patients. However, the absolute increase in risk is small, and in patients with N0 disease the risk is within the low-risk of recurrence category at 3.5%. Minimal ETE has no impact on disease-related mortality, and should not change tumor stage.