Inclusion Criteria:
1. Histologically confirmed non-keratinizing nasopharyngeal carcinoma(WHO II/III).
2. Eligible patients with high-risk locoregionally advanced NPC, defined as AJCC (9th edition) stage T4N1M0 or Tany N2-3M0 disease, or persistent high-risk features after induction chemotherapy (SD, PD, or detectable plasma EBV DNA).
3. ECOG performance status ≤1.
4. Induction and concurrent chemoradiotherapy with the recommended regimen have been completed.
5. No later than 6 weeks after the completion of the last radiotherapy treatment.
6. Adequate hematologic (neutrophil count \> 1.5×10\^9/L, hemoglobin \> 90g/L and platelet count \> 100×10\^9/L), hepatic (alanine aminotransferase, aspartate aminotransferase ≤ 1.5×ULN, bilirubin ≤ 1.5×ULN, alkaline phosphatase \< 2.5×ULN) and renal function (creatinine clearance \> 50 ml/min)
7. Patients must be informed of the investigational nature of this study and give written informed consent.
8. Women of childbearing potential (WOCBP) who are sexually active must be willing to adhere to effective contraception during treatment and for 1 year after the last dose of the study drug. Men who are sexually active with WOCBP must be willing to adhere to effective contraception during treatment and for 1 year after the last dose of the study drug.
Exclusion Criteria:
1. Patients who could not tolerate or were allergic to Becotatug Vedotin.
2. Patients with severe chronic or active infection that must be treated with systemic antibacterial, antifungal, or antiviral therapy before randomization, including but not limited to tuberculosis infection.
3. Prior malignancy except adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer.
4. Pregnancy or lactation (consider pregnancy test in women of child-bearing age and emphasize effective contraception during the treatment period).
5. Interstitial lung disease or pneumonia requiring oral or intravenous steroid therapy within 1 year.
6. Patients who are known to be intolerant or sensitive to any therapeutic agents.
7. Any severe intercurrent disease, which may bring unacceptable risk or affect the compliance of the trial, for example, unstable cardiac disease requiring treatment, renal disease, chronic hepatitis, diabetes with poor control (fasting plasma glucose \> 1.5×ULN), and emotional disturbance.
