EPstein-barr Virus DNA Response to Systemic Therapy for Treatment Adaptation in High Risk NPC (EP-STAR)

The investigators aim to investigate whether incorporating on-treatment EBV DNA surveillance for monitoring tumor responses to treatment and for guiding individuliased treatment adaptation can improve prognosis in nasopharyngeal carcinoma patient . For patients with detectable EBV DNA after one cycle of IC, which then drops to undetectable levels during the following IC cycles (intermediate responders/intermediate relapse risk), the investigators aim to investigate whether additional adjuvant metronomic capecitabine would benefit this subgroup. For patients with detectable EBV DNA after three cycles of IC or with EBV DNA bounce during the induction phase (insensitive to IC/high relapse risk), the investigators aim to investigate whether concurrent administration of anti-PD-1 therapy during the following treatment phases (including concurrent phase and adjuvant phase) can benefit this subgroup.