Background: In 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. Methods: This 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.Results: A 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). Conclusion:Although 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.

We investigated the effects of 13.56 MHz radio frequency (rf) power as a medium frequency power on the plasma characteristics and etch properties of an amorphous carbon layer (ACL) and SiO 2 , using Ar/C 4 F 6 /O 2 gas mixtures in a capacitively coupled plasma (CCP) system operated with pulsed superimposed triple-frequency power of 60 MHz (source)/13.56 MHz (bias)/2 MHz (bias). Compared to the dual frequency rf power of 13.56 MHz (400 W)/2 MHz (900 W) or 60 MHz (400 W)/2 MHz (900 W), the use of triple-frequency rf power of 60 MHz/13.56 MHz/2 MHz (900 W) showed a better anisotropic SiO 2 etch profile, with the higher etch selectivity of SiO 2 over the ACL. We observed the best SiO 2 etch characteristics when the rf powers of 60 MHz and 13.56 MHz were set as 60 MHz (200 W)/13.56 MHz (200 W). In addition, when we varied the pulse duty percentage of 13.56 MHz rf power from 25∼100% (continuous wave (CW)), while keeping the rf powers of 60 MHz/13.56 MHz/2 MHz at 200 W/200 W/900 W, respectively, and while maintaining the pulse duty percentage of 60 MHz and 2 MHz at 50%, the use of the synchronized pulse on/off condition (i.e., the use of 50% duty percentage of 13.56 MHz) also showed the best etch characteristics. The best SiO 2 etch characteristics and the highest etch selectivity of SiO 2 over the ACL (observed for both rf power ratios of 60 MHz (200 W)/13.56 MHz (200 W), and for the triple-frequency pulsing with the synchronized pulse on/off) were related to the higher CF x /F ratios, which increased the fluorocarbon polymer passivation on the ACL surface and SiO 2 sidewall during etching.