Clinical implications of microscopic extrathyroidal extension in patients with papillary thyroid carcinoma

Extrathyroidal extension (ETE) is a poor prognostic factor in papillary thyroid carcinoma (PTC). However, the impact of the degree of ETE, especially microscopic ETE, has not been well established. The purpose of present study was to compare differences in clinicopathological characteristics and clinical outcomes according to the presence or extent of ETE.Data from 381 patients who underwent total thyroidectomy with/without lymph node (LN) dissection for PTC between 2004 and 2010 were analyzed. Clinicopathological features such as age, gender, LN metastasis, capsular invasion, lymphovascular invasion, and recurrence were compared among three groups divided according to degree of ETE: no ETE (n=144), microscopic ETE (n=191), and macroscopic ETE (n=46).Tumor size, LN metastasis, lymphovascular invasion, extent of surgery, and administration of postoperative radioactive iodine (RAI) were significantly correlated with degree of ETE. Especially, among the patients with a primary tumor size ≤4cm, the patients with microscopic ETE showed more LN metastasis and lymphovascular invasion than those without ETE, whereas less LN metastasis and lymphovascular invasion than those with macroscopic ETE. In addition, the microscopic ETE group had a significantly lower 5-year recurrence free survival (RFS) than the no-ETE group (92.1% vs. 99.3%, p<0.001) and a significantly higher 5-year RFS than the macroscopic ETE group (92.1% vs. 65.2%, p<0.001).The degree of ETE is correlated with clinicopathologic features and tumor recurrence. Patients with microscopic ETE have a poorer clinical outcome than those without ETE, but they showed a better outcome than patients with macroscopic ETE.