Tran, Bryan1; Roshan, David2; Abraham, Earl1; Graham, Susannah1; Lehane, Christopher1; Wykes, James1; Campbell, Peter1; Ebrahimi, Ardalan1
1 Head and Neck Unit, Department of Surgery, Liverpool Hospital, Sydney, Australia
2 South Western Sydney Clinical School, UNSW, Sydney, Australia
Background/Purpose: Increasing evidence that microscopic extrathyroidal extension (m-ETE) is not an independent prognostic factor in papillary thyroid carcinoma (PTC) prompted its removal from the 8th edition AJCC T staging (pT8) [1-4]. Tumours staged as T3 in the 7th edition (pT7) based on m-ETE are hence down-staged according to size.
Objectives: We aimed to compare the prognostic performance of pT8 and pT7, particularly in patients ?55 years old without distant metastases, in whom changes to T classification impact TNM stage.
Method: A retrospective analysis of disease-free survival (DFS) in 577 patients with PTC comparing pT8 versus pT7 using the Akaike information criterion (AIC), Harrel’s C-index, proportion of explained variation (r2) and visual inspection for stratification into distinct prognostic groups on Kaplan-Meier curves.
Results: There were 105 T3 patients in pT7, with 74 based on m-ETE. Thirty (28.6%) were down-staged to T1a, 27 (25.7%) to T1b and 17 (16.2%) to T2. In patients ?55 years old without distant metastases, pT8 was inferior to pT7 on the basis of higher AIC, lower C-index (0.68 versus 0.75) and lower r2 (0.34 versus 0.41). In pT8 stage T1a-T3a disease, m-ETE was associated with reduced DFS (HR 2.8, p=0.002) irrespective of tumour size.
Discussion and Conclusion
In our patient population, the prognostic performance of pT8 was inferior to pT7, particularly in patients ?55 years old without distant metastases. Microscopic ETE appears to be an important factor in T staging and consideration should be given to reintroducing this to the AJCC staging if these results are validated.
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