• S Y Park, H I Kim, J-H Kim, J S Kim, Y L Oh, S W Kim, J H Chung, H W Jang, and T H Kim.
• Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Centre, Samsung Medical Centre, Sungkyunkwan University School of Medicine, Seoul, Korea.
• Br J Surg. 2018 Aug 1; 105 (9): 1155-1162.

BackgroundIn the eighth edition of the AJCC staging system for differentiated thyroid carcinoma (DTC), minimal extrathyroidal extension (ETE) is no longer a determinant of T3 category. Instead, gross ETE invading only strap muscles has been designated as a new T3b category. The long-term prognosis of patients with DTC and gross ETE invading only strap muscles was investigated.MethodsThis was a retrospective analysis of patients who underwent thyroidectomy between 1996 and 2005. Differences in cancer-specific and recurrence-free survival according to extent of ETE were assessed.ResultsA total of 3174 patients with DTC were included. No significant differences were observed in 10-year cancer-specific survival among patients with no ETE (98·6 per cent), microscopic ETE (98·3 per cent) and gross ETE invading only strap muscles (98·9 per cent) (P = 0·375). The 10-year recurrence-free survival rate for patients with gross ETE invading only strap muscles (89·2 per cent) was shorter than that for patients with no ETE (93·7 per cent; P = 0·016), but similar to that of patients with microscopic ETE (90·3 per cent). In univariable analysis, patients with gross ETE invading only strap muscles had a significantly higher risk of recurrence than those with no ETE (hazard ratio (HR) 1·67, 95 per cent c.i. 1·10 to 2·55; P = 0·017). In multivariable analysis, gross ETE invading only strap muscles was not an independent predictor of recurrence (HR 1·09, 0·71 to 1·69; P = 0·685).ConclusionAlthough gross ETE invading only strap muscles may provide prognostic information about long-term recurrence, it does not affect mortality. The actual impact of gross ETE invading only strap muscles will be important in revising the staging system in the future.© 2018 BJS Society Ltd Published by John Wiley & Sons Ltd.

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