Becotatug Vedotin Plus Sintilimab in Locoregionally Advanced NPC

Inclusion Criteria: 1. Voluntarily participate in the study and sign the informed consent form in writing. 2. Aged 18-70 years, male or non-pregnant female. 3. Pathologically confirmed as nasopharyngeal non-keratinizing carcinoma (differentiated or undifferentiated type, i.e., WHO type II or III). 4. Staged as anyT N2-3 or T4N1 (9th AJCC/UICC staging) without distant metastasis. 5. ECOG performance status score of 0-1. 6. Hemoglobin (HGB) ≥ 90 g/L, neutrophil count ≥ 1.5×10⁹/L, and platelet (PLT) count ≥ 100×10⁹/L. 7. Liver function: Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 times the upper limit of normal (ULN), and total bilirubin ≤ 1.5 times ULN. 8. Normal renal function: Creatinine clearance rate ≥ 60 ml/min (calculated using the Cockcroft-Gault formula). 9. Sexually active females of childbearing potential must agree to use effective contraceptive measures during treatment and for 1 year after the last administration of the study drug. Males who have sexual relations with females of childbearing potential must also agree to use effective contraceptive measures during treatment and for 1 year after the last administration of the study drug. Exclusion Criteria: 1. Aged \> 70 years or \< 18 years. 2. Patients with recurrent or distant metastatic nasopharyngeal carcinoma. 3. Pathologically confirmed as keratinizing squamous cell carcinoma (WHO type I). 4. Patients who have previously received radiotherapy or systemic chemotherapy. 5. Positive for hepatitis B surface antigen (HBsAg) with hepatitis B virus DNA \> 1000 copies/mL or 200 IU/mL. 6. Positive for hepatitis C virus antibody (anti-HCV). 7. Patients with active autoimmune diseases, excluding type 1 diabetes mellitus, hypothyroidism controlled by replacement therapy, and skin diseases that do not require systemic treatment (e.g., vitiligo, psoriasis, or alopecia). 8. Patients who received systemic glucocorticoids (equivalent to prednisone \> 10 mg/day) or other immunosuppressive therapy within 28 days prior to signing the informed consent form. Patients who received systemic glucocorticoids equivalent to prednisone ≤ 10 mg/day, inhaled or topical glucocorticoids are eligible for enrollment. 9. Patients with a history of active tuberculosis within the past year; patients with active tuberculosis that has been adequately treated for more than one year are eligible for enrollment. Patients with a history of other malignant tumors (except cured basal cell carcinoma or carcinoma in situ of the cervix). 10. Patients with a history of interstitial lung disease. 11. Patients who received live vaccines within 30 days prior to signing the informed consent form or plan to receive live vaccines in the near future. 12. Pregnant or lactating females. 13. Patients with a history of other malignant tumors within the past 5 years, except carcinoma in situ, adequately treated non-melanoma skin cancer, and papillary thyroid cancer. 14. Patients with known hypersensitivity to any component of gemcitabine, cisplatin, becotatug vedotin, or sintilimab. 15. Patients with known history of HIV infection. 16. Any other conditions deemed by the investigator to potentially affect the patient's ability to sign the informed consent form, cooperate with and participate in the study, or interfere with the interpretation of results, including symptomatic heart failure, unstable angina pectoris, myocardial infarction, active infections requiring systemic treatment, mental illnesses, or family/social factors.