Objectives: Extrathyroidal invasion is one of the most significant risk factors for patients with papillary thyroid carcinoma (PTC). The purpose of this study was to evaluate a novel definition of extrathyroidal invasion for patients with PTC as a method for predicting a patient's prognosis.
Methods: The prospective study was conducted for consecutive 930 patients with primary PTC who received surgery during 1993-2009. We defined only patients who had preoperative recurrent laryngeal nerve palsy or patients in whom the tumor had invaded to the mucosa of the trachea and/or esophagus as Ex3. Patients with minimal invasion were classified as Ex1, and patients with massive invasion, when we could shave off the tumors, were classified as Ex2. Patients without extrathyroidal invasion were classified as Ex0.
Results: Patients classified Ex3 showed significantly shorter disease-free survival (p = 0.03) and disease-specific survival (p = 0.007) than patients classified Ex2. The time to recurrence at resection sites was shorter in patients classified Ex3 than in patients classified Ex2 (p = 0.02). The time to death due to distant metastasis of patients classified Ex3 was significantly shorter than that of patients classified Ex2 (p = 0.02). Within the patients classified Ex3, disease-specific survival of patients with invasion to other nearby structures was shorter than that of patients with invasion to only recurrent laryngeal nerve (p = 0.008).
Conclusions: The degree and site of invasion is an important prognostic factor for PTC. Our novel classification of extrathyroidal invasion is valuable in predicting the prognosis of PTC.