CNG (Collaborative Nasopharyngeal Carcinoma Group) stage: Improved prognostic stratification of nasopharyngeal carcinoma and association with Epstein-Barr virus DNA in the intensity-modulated radiation therapy era.

Abstract

Current 8th AJCC stage is less effective in differentiating survival for nasopharyngeal carcinoma (NPC) in the intensity-modulated radiotherapy era. This study aims to evaluate the performance of CNG (Collaborative Nasopharyngeal Carcinoma Group) stage, a clinical downstaging of NPC based on the 7th AJCC stage, in predicting prognosis compared with the AJCC stage. In this prospective observational study (ClinicalTrials.gov Identifier: NCT03529279), 1930 patients were restaged based on the 7th stage: CNG Stage I: Stage I, II, and III-nonT3N2; CNG Stage II: III-T3N2, IVA, and IVB; CNG Stage III: IVC. Kaplan-Meier method and the log-rank test were performed. The 5-year overall survival (OS) of patients with CNG Stage I, II, and III was 97.0 %, 91.4 %, and 72.1 %, and survival curves of different stage groups were well-separated (all p < 0.001). The OS curves for 7th and 8th Stage I, II, and III almost overlapped. In patients with pre-treatment plasma EBV DNA > 0 and ≥ 1000 copies/ml, overall and inter-group OS differences were observed in CNG stage, while not shown in 7th and 8th stages. Among CNG Stage I, II, and III, the proportion of patients with EBV DNA = 0 was gradually decreasing (30.9 % vs 10.8 % vs 3.4 %), while the proportion of EBV DNA ≥ 1000 was gradually increasing (33.3 % vs 60.0 % vs 84.8 %, p < 0.001). The CNG staging system presents a more accurate segregation of survival rates than the 7th and 8th editions, and it is well aligned with EBV DNA. Further studies of the staging system are warranted.