Comparison of the seventh and eighth editions of the UICC/AJCC staging system for nasopharyngeal carcinoma: analysis of 1317 patients treated with intensity-modulated radiotherapy at two centers

BACKGROUND: In the intensity-modulated radiotherapy (IMRT) era, great improvement has been made in survival of nasopharyngeal carcinoma (NPC). The 7th edition of the International Union against Cancer/American Joint Committee on Cancer (UICC/AJCC) staging system seems “outdated ” as it mainly based on the study in 2D/3D era, and thus the 8th edition has made some amendments according to recent studies. We aimed to compare and evaluate these two editions of staging system for NPC in patients treated with intensity-modulated radiotherapy. METHODS: A total of 1317 patients with biopsy-proven, non-metastatic NPC treated with IMRT between 2009 and 2014 at two institutions were retrospectively assessed. All patients were assessed by magnetic resonance imaging and restaged according to the 7th and 8th editions. Prognostic factors for local relapse-free survival (LRFS), distant metastasis-free survival (DMFS), disease-free survival (DFS) and overall survival (OS) were assessed and compared using the Kaplan-Meier method and log-rank test. The Cox proportional hazards model was also used to calculate the hazard ratio (HR). RESULTS: In both 7th and 8th edition, insignificant difference could be observed between T2 and T3 disease, T2 and T4 disease (all P > 0.05) for LRFS, while the difference of LRFS between T3 and T4 disease was significant in the previous edition (P = 0.001) but insignificant (P = 0.279) after revision. For OS, highly similar survival curve could be seen between T2 and T3 disease in both edition (all P > 0.1). DMFS and OS were not significantly different between N3a and N1-3b categories of the 7th edition (all P > 0.05). In contrast, obvious segregation was observed between N3 and the other N categories after the revision and combination in the 8th edition (all P < 0.05). DFS and OS were not significantly different between stage IVA and IVB of the 7th edition (P = 0.057 and P = 0.365, respectively); therefore, combining these stages in the 8th edition was reasonable. CONCLUSION: The overall stages and N categories of the 8th edition of the UICC/AJCC staging system provide better segregation of survival outcomes than the 7th edition. The 8th edition is also more clinically applicable as it has reduced ambiguity and revised out-of-date definitions. However, the T categories need further optimizing as the 8th edition failed to solve the problem of similar survival between adjacent T-classification, which has been exited since 7th edition.