Microscopic positive margins strongly predict reduced disease-free survival in pT4a papillary thyroid cancer

Background: Although microscopic positive margins appear to have no independent prognostic impact in papillary thyroid cancer (PTC), this may not be the case in pT4a tumors. Methods: Retrospective analysis of 610 patients with PTC, 39 with pT4a tumors, to determine if microscopic positive margins impact disease-free survival (DFS) in pT4a PTC. Results: On univariate analysis, microscopic positive margins were not associated with reduced DFS in patients with no extrathyroidal extension (ETE) (hazard ratio [HR], 1.7; P = 0.32), microscopic ETE (HR, 1.6; P = 0.36), or macroscopic ETE limited to strap muscles (HR, 1.2; P = 0.87). In contrast, microscopic positive margins were associated with reduced DFS in T4a disease (HR, 4.1; P = 0.04). Disease recurrence was nodal, distant, or biochemical, and did not occur directly at the site of positive margins. Conclusion: Although microscopic positive margins do not influence DFS in the majority of patients with PTC, they are associated with a fourfold increased risk of recurrence in pT4a disease.