Prognostic value of the eighth edition AJCC TNM classification for differentiated thyroid carcinoma
Introduction
The American Joint Committee on Cancer (AJCC) tumor, node, and metastasis (TNM) system is the most widely used indicator of cancer mortality in patients with differentiated thyroid carcinoma (DTC) [1], [2]. Unlike most malignancies, age at diagnosis is almost always identified as an independent predictor of cancer mortality in DTC. Accordingly, the TNM system of DTC has incorporated both anatomic and nonanatomic (an age cutoff of 45 years) prognostic factors since its second edition was published in 1983 [3]. The system was subsequently validated in several different cohorts and predicted cancer mortality reasonably well [4], [5].
Several groups, including ours [6], have proposed modifications to the staging system to improve its prognostic validity. For example, moving the age cutoff point from 45 to 55 years lead to down-staging of 12% of patients in a multicenter retrospective study [7]. Furthermore, a survival difference was not found in tumors with microscopic extrathyroidal extension (ETE), a determinant of T3 disease that designated older patients as stage III, compared with intrathyroidal tumors [8], [9].
Accumulating evidence informed the revision of the TNM classification for DTC, resulting in several changes from the seventh edition, particularly regarding the age cutoff point, T categories, and stage groupings [10]. It is unclear at present whether these changes would significantly improve the prognostic ability. The aim of this study is to evaluate the predictive ability of the forthcoming eighth edition of the AJCC TNM classification compared with the seventh edition for cancer-specific survival (CSS) in a large cohort of patients with DTC who underwent thyroidectomy.
Section snippets
Patient enrollment and data collection
This study included patients who underwent thyroidectomy for DTC between 1996 and 2005 at Samsung Medical Center, Seoul, Korea. Only patients with histologically confirmed DTC [papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC), and Hurthle cell thyroid carcinoma (HTC)] were included, and patients with poorly differentiated thyroid carcinoma were excluded. The study protocol was approved by the Institutional Review Board of Samsung Medical Center (IRB No. 2016-05-053). The
Clinicopathologic characteristics of the study population
A total of 3176 patients were enrolled in this study. Patient characteristics are described in Table 1. All patients were Korean, and a female predominance was observed (86.5%). The median age at diagnosis of DTC was 46.0 years (IQR 38.0–54.8 years). The majority of patients (97.3%) had PTC, and 85 (2.7%) had FTC (including HTC). The mean size of the primary tumor was 1.5 cm, and 436 (13.7%) patients had gross ETE (T3b or T4 in the eighth edition T categories). Cervical lymph node metastases were
Discussion
In the past 20 years, the incidence of DTC has dramatically increased around the globe mainly due to the facilitated diagnosis of small (<2 cm) PTCs by high-resolution neck ultrasound [16], [17], [18]. However, prediction of long-term CSS to guide the clinical management of patients with DTC is still unsatisfactory, and the current seventh edition TNM stage groups do not adequately portray the outcome of these patients [19]. Because of the changing epidemiology and stage migration effect induced
Financial disclosure
This research was supported by a grant (CRO113031) and a CRP-achievement grant (OTA1603111) from Samsung Medical Center.
Role of the funding source
The funder had no role in the design or conduct of the study, the collection, analysis or interpretation of the data, or in the preparation, review, or approval of the manuscript.
Conflict of interest statement
All authors indicated no potential or actual conflicts of interest.
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