Comparison of the eighth and ninth editions of American Joint Committee on Cancer/Union for International Cancer Control staging for non-metastatic nasopharyngeal carcinoma.

<b>Introduction:</b> The ninth edition of the American Joint Committee on Cancer/Union for International Cancer Control (AJCC/UICC) tumor-node-metastasis (TNM) system for patients with non-metastatic nasopharyngeal carcinoma (NPC) was based on data from endemic regions, and it required validation for application to non-endemic regions. <br><br><b>Aim:</b> The aim of this study was to compare the performance of the 8<sup>th</sup> and the 9<sup>th</sup> editions of the AJCC/UICC TNM system for patients with non-metastatic NPC from non-endemic regions. <br><br><b>Materials and methods:</b> Using the Surveillance, Epidemiology, and End Results (SEER) database, 2004-2021, we re-classified NPC patients using 8<sup>th</sup> and the 9<sup>th</sup> edition staging based on surrogate markers of advanced radiological extranodal extension (nodes described as "fixed") and compared the prediction performance of both staging editions for overall survival (OS) and cancer specific survival (CSS). <br><br><b>Results:</b> Our analysis included 4981 patients with a median follow-up of 99.0 months. Comparing the 9<sup>th</sup> version of AJCC/UICC (TNM-9) with TNM-8, only 29 (1.8%) patients with N1 and 47 (3.3%) patients with N2 were upstaged to N3 in TNM-9. In comparisons based on OS, TNM-9 did not outperform TNM-8 with regard to hazard consistency (2.2326 <i>vs</i> 1.9160), hazard discrimination (1.4092 <i>vs</i> 1.0947), sample size balance (0.3476 <i>vs</i> 0.3398), and percent variance explained (0.2704 <i>vs</i> 0.2704). The area under the receiver operating characteristic curve (AUC) values of TNM-9 and TNM-8 were 0.5299 and 0.5330 for OS (P = 0.549), respectively. The AUC values of TNM-9 and TNM-8 were 0.5332 and 0.5357 for CSS (P = 0.345), respectively. <br><br><b>Conclusions:</b> Restaging according to TNM-9 criteria involved only minor changes in the distribution of nodal (N) categories. Neither the TNM-9 nor the TNM-8 staging system demonstrated adequate overall discrimination between each stage group classification in terms of OS and CSS for patients with non-metastatic NPC from a non-endemic region.