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BACKGROUND:The prognosis of patients who have Epstein-Barr virus (EBV)-related nasopharyngeal carcinoma (NPC) in which the tumor tissues harbor EBV have a better prognosis than those without EBV-related NPC. Therefore, the eighth edition of the TNM staging system could be modified for EBV-related NPC by incorporating the measurement of plasma EBV DNA. METHODS: In total, 979 patients with NPC who received intensity-modulated radiotherapy (IMRT) were retrospectively reviewed. Recursive partitioning analysis was conducted based on tumor (T) classification, lymph node (N) classification, and EBV DNA measurement to derive objectively the proposed stage groupings. The validity of the proposed stage groupings was confirmed in a prospective cohort of 550 consecutive patients who also received with IMRT. RESULTS: The pretreatment plasma EBV DNA level was identified as a significant, negative prognostic factor for progression-free survival and overall survival in univariate analysis (all P < .001) and multivariate analysis (all P < .05). Recursive partitioning analysis of the primary cohort to incorporate EBV DNA generated the following proposed stage groupings: stage RI (T1N0), RIIA (T2-T3N0 or T1-T3N1, EBV DNA ≤2000 copies/mL), stage RIIB (T2-T3N0 or T1-T3N1, EBV DNA >2000 copies/mL; T1-T3N2, EBV DNA ≤2000 copies/mL), stage RIII (T1-T3N2, EBV DNA >2000 copies/mL; T4N0-N2), and stage RIVA (any T and N3). In the validation cohort, the 5-year progression-free survival rate was 100%, 87.9%, 76.7%, 68.7%, and 50.4% for proposed stage RI, RIIA, RIIB, RIII, and RIV NPC, respectively (P < .001). Compared with the eighth edition TNM stage groupings, the proposed stage groupings incorporating EBV DNA provided better hazard consistency, hazard discrimination, outcome prediction, and sample size balance. CONCLUSIONS: The proposed stage groupings have better prognostic performance than the eighth edition of the TNM staging system. EBV DNA titers should be included in the TNM staging system to assess patients who have EBVrelated NPC. Cancer 2019;125:79-89.

In this study, we evaluated the 8th edition of the Union for International Cancer Control (UICC)/AJCC staging system for nasopharyngeal carcinoma (NPC) in an endemic area, with the aim of validating its applicability and providing further information for future refinements. A total of 1,790 patients with newly diagnosed, non-distant metastatic, histologically proven NPC treated with intensity-modulated radiotherapy (IMRT) were retrospectively reviewed. The performance of various staging systems was compared using the Akaike information criterion (AIC) and Harrell's concordance index (c-index). For N (node) category, the survival curves of different groups according to the 8th edition were well-separated, and the prognostic model predicted outcomes fairly well. The 8th edition had higher AIC and c-index values for all end points than the 7th edition. However, probably due to the improved locoregional control provided by IMRT, the survival curves for T2 and T3 almost overlapped, without significant differences in locoregional failure-free survival (=.606) and disease-free survival (=.735). Due to the difficultly of differentiating T2 and T3, the AIC and c-index values were similar for the T categories of the 7th and 8th editions. Similarly, the overall survival and disease-free survival curves for stage II and III disease were not clearly separated for either the 8th or 7th editions. The 8th edition of the UICC/AJCC staging system for NPC enables more accurate prediction of treatment outcomes. However, several limitations need to be addressed in future editions, and it would be reasonable to further optimize the T category classification.

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Different dosimetric parameters may hinder the dosimetric research. The present recommendation and atlas, may help reach a consensus on subjective interpretation of OARs delineation to reduce inter-institutional differences in NPC patients.