Minimal extrathyroidal extension does not affect survival of well-differentiated thyroid cancer

Differentiated thyroid cancer (DTC) with minimal extrathyroidal extension (MEE) is classified as stage III regardless of the tumor size. In this study, we aim to examine the effect of MEE on the overall survival and management of this population. A retrospective cohort study was performed, which utilized the National Cancer Database (NCDB), 2004-2012. The study population included patients, aged ≥ 45 years, who underwent surgery for DTC (pT3N0M0) with MEE compared to that in patients with pT2N0M0. A total of 9556 patients were included. These were divided into four groups, 4410 patients with pT2N0M0 (Group 1: T ≤ 4 cm without MEE), 3274 with pT3N0M0 (Group 2: T ≤ 4 cm with MEE), 447 with pT3N0M0 (Group 3: T > 4 cm with MEE) and 1430 patients with pT3N0M0 without MEE (Group 4: T > 4 cm without MEE). Median follow-up time was 46.7 months (interquartile range: 27.8-72.1). Patients in Group 2 (T ≤ 4 cm with MEE) had no significant worse survival compared to patients in Group 1 (T ≤ 4 cm without MEE) (P = 0.85), whereas Groups 3 and 4 (T > 4 cm), both had significantly lower survival (P < 0.001) with no difference between the two groups. Total thyroidectomy was associated with improved overall survival compared to that in lobectomy in Group 4 (T > 4 cm without MEE). Radioiodine utilization was associated with improved survival only with tumors larger than 4 cm with or without MEE. In DTC patients aged older than 45 years of age with tumor size less than 4 cm, MEE has no survival significance. Tumor size is an independent prognostic marker regardless of MEE status. Our data support re-evaluation of the current staging system.