Extrathyroidal extension (ETE) is a risk factor for the recurrence of a papillary thyroid carcinoma (PTC). In the TNM 6^th classification system, an extrathyroidal invasion of a differentiated thyroid carcinoma has been classified as T3 (minimal invasion), T4a (extended invasion), and T4b (more extensive unresectable invasion) according to tumor invasion. We investigated the clinicopathologic characteristics, recurrence, and disease-free survival (DFS) of minimal ETE (mETE).

We retrospectively evaluated 332 patients who underwent a thyroidectomy for PTC from January 2005 to December 2006.

Of the 332 patients, 103 (31.0%) were found to have a PTC with mETE and 229 (69.0%) patients had a PTC without mETE. In PTC, mETE was related to gender, tumor size, multifocality, Lymph node (LN) metastasis, underlying Hashimoto's thyroiditis, and surgery. But there is no significant difference in age, recurrence, and LN metastasis between the mETE and No mETE groups. Multivariate analysis demonstrated that LN metastasis (odds ratio=2.273; 95% confidence interval 1.280~4.037) was recognized as an independent factor for mETE (P=0.005). Disease-free survival was not significantly different between patients with and without mETE (P=0.153). We analyzed the effect of LN metastasis in groups with and without mETE. Based on the presence or absence of LN metastasis, disease-free survival (DFS) rates between each group showed no significant differences.

Minimal ETE had no impact on DFS in patients with PTC. Therefore, an appropriate surgical approach and postoperative follow-up are required for tumors with mETE.