A Study of Anti-PD-1 Antibody With or Without BL-B01D1 as Maintenance Therapy Following Anti-PD-1 Antibody Plus Chemotherapy for the First-line Treatment of Recurrent or Metastatic Nasopharyngeal Carcinoma (PANKU-NPC02)

Inclusion Criteria: 1. Voluntarily sign the informed consent form and comply with the protocol requirements; 2. Age ≥ 18 years; 3. Expected survival time ≥ 3 months; 4. Trial participants with nasopharyngeal carcinoma confirmed by histopathology and/or cytology, either initially diagnosed with metastatic disease or relapsed after curative-intent treatment; 5. Agree to provide tumor tissue samples obtained at or after the diagnosis of recurrent or metastatic disease; 6. Must have at least one measurable lesion as defined by RECIST v1.1; 7. Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1; 8. Toxicities from prior anti-tumor therapy must have recovered to ≤ Grade 1 as defined by NCI-CTCAE v6.0; 9. No severe cardiac dysfunction, with left ventricular ejection fraction ≥ 50%; 10. Organ function levels must meet the required criteria; 11. Urine protein ≤ 1+ or \< 1000 mg/24h; 12. For premenopausal women of childbearing potential, a pregnancy test must be performed within 7 days before starting treatment; serum pregnancy test must rule out pregnancy; they must not be breastfeeding and must use highly effective contraceptive methods throughout the entire treatment period and for 7 months after the last dose. For male trial participants whose partners are women of childbearing potential, adequate barrier contraception must be used throughout the entire treatment period and for 7 months after the end of treatment. Exclusion Criteria: 1. Trial participants who have received prior systemic therapy; 2. Those who have received prior therapy targeting the mechanism of tumor immuno-oncology; 3. Those who have previously received antibody-drug conjugates (ADCs) using topoisomerase I inhibitors as the toxin, or EGFR- and/or HER3-targeting antibodies/ADCs; 4. Trial participants who have received systemic immunostimulatory agents within 4 weeks prior to the first dose; 5. Those who have received radical radiotherapy, major surgery, or extensive-field radiotherapy within 4 weeks prior to study randomization; 6. History of severe cardiac or cerebrovascular disease; 7. Those receiving long-term systemic corticosteroid therapy (e.g., prednisone \>10 mg/day) prior to the first dose; 8. Active autoimmune diseases and inflammatory diseases; 9. Unstable thrombotic events requiring therapeutic intervention within 6 months prior to screening; 10. Prolonged QTc interval, complete left bundle branch block, third-degree atrioventricular block, or frequent and uncontrolled arrhythmias; 11. Diagnosis of active malignancy within 3 years prior to study randomization; 12. Hypertension inadequately controlled by two antihypertensive agents; 13. Trial participants with poorly controlled blood glucose; 14. History of interstitial lung disease (ILD) requiring steroid therapy, current ILD, or radiation pneumonitis of Grade ≥2; 15. Concurrent pulmonary diseases resulting in clinically severe impairment of respiratory function; 16. Active central nervous system (CNS) metastases; 17. Severe infection occurring within 4 weeks prior to study randomization; 18. Trial participants with massive serosal cavity effusion, symptomatic serosal cavity effusion, or poorly controlled serosal cavity effusion; 19. Imaging findings indicating tumor invasion or encasement of abdominal, thoracic, or cervical structures; 20. Severe, non-healing wounds, ulcers, or bone fractures within 4 weeks prior to signing informed consent; 21. Trial participants with clinically significant bleeding or obvious bleeding tendency within 4 weeks prior to signing informed consent; 22. Trial participants with inflammatory bowel disease, history of extensive bowel resection, history of immune-mediated enteritis, intestinal obstruction, or chronic diarrhea; 23. Trial participants with a history of allergy to recombinant humanized antibodies or hypersensitivity to the investigational drug; 24. History of autologous or allogeneic stem cell transplantation; 25. Positive for human immunodeficiency virus (HIV) antibodies, active hepatitis B virus (HBV) infection, or hepatitis C virus (HCV) infection; 26. History of severe neurological or psychiatric disorders; 27. Receipt of other unapproved investigational drugs or treatments within 4 weeks prior to study randomization; 28. Trial participants who plan to receive, or have received, live vaccines within 28 days prior to study randomization; 29. Other conditions deemed by the investigator to make the participant unsuitable for participation in this clinical trial due to complications or other circumstances.