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.