Assessment of the prognostic value and N1b changes of the eighth TNM/AJCC staging system for differentiated thyroid...

The aim of this study was to evaluate the prognostic veracity for disease-specific survival (DSS) of the eighth edition of the American Joint Committee on Cancer/Union for International Cancer Control tumor-node-metastasis staging system (TNM-8) compared with the seventh edition (TNM-7) in a Chinese population of patients with differentiated thyroid carcinoma (DTC) and to evaluate the impact of N1b redefinition and reclassification on prediction of survival.

A total of 569 DTC patients who underwent thyroid surgery in two Chinese hospitals were included in analysis to assess the predictive accuracy and N1b changes of TNM-8. Data from the Surveillance, Epidemiology and End Results (SEER) program were applied to validate the findings on N1b changes of TNM-8. Unadjusted DSS was calculated using the Kaplan-Meier method. Multivariable Cox proportional hazards models were used to evaluate the association of stage and lymph node metastasis (LNM) status with survival. The proportion of variation explained (PVE), Akaike information criterion (AIC), and Bayesian information criterion (BIC) were evaluated to compare model performance.

When TNM-8 was applied, 39.7% of patients were downstaged relative to TMN-7. In comparison of TNM-7 and TMN-8, the PVE was 18.68% and 22.33%, the AIC was 704.22 and 680.50, and the BIC was 702.98 and 679.24, respectively. In 569 Chinese patients with DTC, levels I-V LNM was significantly related to poorer DSS compared with N0 and level VI LNM. Among patients aged ≥ 55 years, those with levels I-V and VII LNM had significantly worse DSS than those with N0 and Level VI LNM. In the SEER dataset, patients with levels I-V and VII LNM had significantly worse DSS compared with those with N0 and Level VI LNM, especially in older patients (age ≥ 55 years).

TNM-8 staged a significant number of Chinese patients into lower stages and improved the accuracy of predicting DSS compared with TNM-7. However, changes in lateral LNM definition and classification of TNM-8 have a significant prognostic implication for patients with DTC, especially older patients (≥ 55 years). Our data suggest that a modified TNM staging system would be more useful for predicting mortality and determining a proper treatment strategy in patients with DTC.