Toripalimab vs. Placebo Wtih GP Induction Chemotherapy in Locoregionally Advanced Nasopharyngeal Carcinoma

The main questions it aims to answer are: 1. Does the combination of GP induction chemotherapy and toripalimab improve the 3-year progression-free survival (PFS) compared to GP induction chemotherapy with placebo? 2. What are the differences in CR after induction therapy, 3-year overall survival (OS), locoregional progression, and distant progression between the two groups? 3. What are the differences in safety between the two groups? 4. Are there predictive biomarkers of therapeutic efficacy, such as changes in EBV DNA or immune parameters, that correlate with treatment outcomes? Researchers will compare the GP + toripalimab group with the GP + placebo group to see if the toripalimab combination shows superior efficacy. Participants will: Receive either GP chemotherapy with toripalimab or GP chemotherapy with placebo as induction therapy. Undergo concurrent chemoradiotherapy ± adjuvant metronomic capecitabine following induction therapy. Be monitored closely for safety and efficacy outcomes.