Elsevier

Oral Oncology

Volume 71, August 2017, Pages 81-86
Oral Oncology

Prognostic value of the eighth edition AJCC TNM classification for differentiated thyroid carcinoma

https://doi.org/10.1016/j.oraloncology.2017.06.004Get rights and content

Highlights

  • Prognostic value of the proposed eighth edition AJCC TNM in DTC is uncertain.

  • The eighth edition resulted in down-staging in 40% of patients than the seventh.

  • The eighth edition can lead to superior prognostication for long-term CSS.

Abstract

Background

The prognostic value of the proposed eighth edition of the American Joint Committee on Cancer (AJCC) tumor, node, and metastasis (TNM) classification is currently unclear. The aim of the study was to evaluate the prognostic value of the eighth edition of the AJCC TNM classification.

Methods

We retrospectively assessed 3176 patients with differentiated thyroid carcinoma (DTC) who underwent thyroidectomy at a tertiary Korean hospital from 1996 to 2005. Cancer-specific survival (CSS) was analyzed using the Kaplan–Meier method and compared using the log-rank test. Performance of the eighth edition TNM with respect to prediction of CSS was assessed against the current seventh edition.

Results

Upon reclassification according to the eighth edition, 37.6% of patients were down-staged. The proportions of stage I and II tumors increased from 61.9% to 81.1% and from 1.7% to 16.0%, respectively, whereas those of stage III and IVB (formerly IVC in the seventh edition) decreased from 27.6% to 2.3% and 0.8% to 0.5%, respectively. The proportions of variance explained (PVEs) for the ability of the eighth and the seventh edition to predict CSS were 3.9% and 2.9%, respectively. The C-index values were 0.765 (95% confidence interval 0.764–0.766) for the eighth edition and 0.736 (0.735–0.737) for the seventh edition.

Conclusion

Our results demonstrate that the eighth edition TNM more accurately predicts CSS for patients with DTC than does the seventh edition.

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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