GAPP Induction and Concurrent Chemoradiotherapy for High-risk Locoregionally Advanced NPC.

Inclusion Criteria: * Voluntary participation and signed informed consent. * Age 18-65 years, male or non-pregnant female. * Pathologically confirmed non-keratinizing nasopharyngeal carcinoma (differentiated or undifferentiated type, i.e., WHO type II or III). * Previously untreated patients with no history of other malignancies; initial treatment for nasopharyngeal carcinoma. * Stage III: TanyN3M0 / T4N0-2M0 (9th AJCC/UICC staging system). * ECOG performance status 0-1, with no severe dysfunction of vital organs (heart, lung, liver, kidney, etc.). * Hemoglobin (HGB) ≥90 g/L, white blood cell count (WBC) ≥4.0×10\^9 /L, platelet count (PLT) ≥100×10\^9/L. * Liver function: ALT and AST \<2.5× upper limit of normal (ULN); total bilirubin \<2.0×ULN. * Renal function: serum creatinine \<1.5×ULN. Exclusion Criteria: * Patients with recurrent or distant metastatic nasopharyngeal carcinoma. * Pathologically confirmed keratinizing squamous cell carcinoma (WHO type I). * Receipt of systemic or topical glucocorticoid therapy within 4 weeks prior to enrollment. * Participation in another clinical trial of an investigational drug within 3 months prior to treatment. * Known history of allogeneic organ transplantation or allogeneic hematopoietic stem cell transplantation. * Patients with idiopathic pulmonary fibrosis, drug-induced pneumonitis, organizing pneumonia (i.e., bronchiolitis obliterans), radiation pneumonitis that is clinically symptomatic or requires steroid therapy, active pneumonitis, or other moderate-to-severe pulmonary diseases that significantly affect lung function. * Comorbidities requiring long-term immunosuppressive medication or systemic/topical corticosteroids at immunosuppressive doses. * Prior use of anti-PD-1, anti-PD-L1, anti-PD-L2, or anti-CTLA-4 antibodies (or any other antibodies targeting T-cell co-stimulatory or checkpoint pathways) with documented disease progression at the time of study entry. * Presence of any active autoimmune disease or history of autoimmune disease (including but not limited to: interstitial pneumonia, uveitis, enteritis, hepatitis, hypophysitis, nephritis). Patients with vitiligo or childhood asthma that has completely resolved and requires no intervention in adulthood may be included; patients requiring bronchodilators for medical management of asthma are excluded. * HIV-positive; HBsAg-positive with detectable HBV DNA copy number (quantitative detection ≥1000 cps/mL); positive hepatitis C antibody (HCV Ab) with detectable HCV RNA. * Receipt of any anti-infective vaccine (e.g., influenza vaccine, varicella vaccine) within 4 weeks prior to enrollment. * Positive pregnancy test in women of childbearing potential, or lactating women. * Inability to comply with scheduled follow-up due to psychological, social, family, or geographical reasons.