Serial early post-IMRT undetectable plasma EBV DNA to predict outcomes in non-metastatic nasopharyngeal cancer

Abstract

BACKGROUND: The relationship between early undetectable plasma EBV DNA after intensity-modulated radiation therapy (IMRT) for NPC and long-term survival remains unclear. Early post-IMRT undetectable plasma EBV DNA is a proposed efficacy endpoint which warrants investigation as a predictor of long-term survival. We prospectively explored the predictive power of post-IMRT 8th week and 6th month undetectable plasma EBV DNA for 3-year survival outcomes in patients with non-metastatic NPC. METHODS: Two hundred and sixty patients with non-metastatic NPC were treated with IMRT +/- concurrent /induction/adjuvant platinum-based chemotherapy. Plasma EBV DNA was taken at diagnosis and then 8 weeks and 6 months after IMRT. Time-dependent Receiver-Operating Characteristics (TD-ROC) were used to obtain Cτ indices. Cox regression models identified interaction between undetectable post-IMRT 8th week and 6th month plasma EBV DNA and outcomes including progression-free survival (PFS), cancer-specific survival (CSS) and overall survival (OS). RESULTS: A strong relationship was shown between post-IMRT 8th week and 6th month undetectable plasma EBV DNA with PFS, CSS and OS (TD-ROC revealing higher Cτ indices for stage IVA–B compared to stage I–III). Cox regression showed that post-IMRT 8th week and 6th month undetectable plasma EBV DNA were prognostic of PFS (p < 0.001 and p < 0.001, respectively), CSS (p = 0.006 and p = 0.004, respectively) and OS (p = 0.039 and p = 0.012, respectively). Baseline plasma EBV DNA was not prognostic of any survival outcome. CONCLUSIONS: Our study showed a strong relationship between post-IMRT 8th week and 6th month undetectable plasma EBV DNA and 3-year survival outcomes. This suggested the use of early plasma EBV DNA as a predictor of survival in this setting.