Minimal Extrathyroidal Extension in Papillary Thyroid Microcarcinoma Is an Independent Risk Factor for Relapse Through Lymph Node and Distant Metastases

Minimal extrathyroidal extension (mETE) of papillary thyroid microcarcinoma (PTMC) is no longer considered in the new eighth edition of the staging manual of the American Joint Committee on Cancer and the International Union Against Cancer. Therefore, PTMC with mETE previously staged as pT3 will now be staged as pT1a and most likely not receive adjuvant radioiodine therapy. However, it remains unclear whether mETE is associated with higher aggressiveness in PTMC. Therefore, the aim of this study was to investigate whether mETE is associated with a higher risk of lymph node metastases (LNMs) or distant metastases. Methods: In total, 721 patients with PTMC presenting at our department for postoperative counseling from May 1983 to August 2012 were included in this retrospective analysis (median follow-up time, 9.30 y). The impact of mETE on the presence of LNMs at thyroidectomy and relapse through LNMs and distant metastases was assessed by logistic regression and Fine-Gray model analyses. Results: mETE was present in 10.7% (n = 77) of patients and was an independent risk factor for LNMs at thyroidectomy, with an adjusted odds ratio of 4.33 (95% CI, 2.02-9.60; P < 0.001) in multivariable analysis. Patients with mETE had significantly more relapses through LNMs (over 5 y: 13.1% vs. 1.25%; P < 0.001) and distant metastases (over 5 y: 7.8% vs. 1.1%; P < 0.001) than did patients without mETE. mETE was an independent risk factor for relapse through LNMs and distant metastases in multivariable analysis (hazard ratio of 7.78 and 95% CI of 2.87-21.16 for LNMs [P < 0.001]; hazard ratio of 4.09 and 95% CI of 1.25-13.36 for distant metastases [P = 0.020]). Conclusion: mETE is a statistically significant and independent risk factor for relapse through LNMs and distant metastases in PTMC. Therefore, future studies should evaluate whether patients with mETE and PTMC might benefit from intensified surveillance and therapy.