This study aims to explore the efficacy and safety of tislelizumab combined with capecitabine in nasopharyngeal carcinoma patients with residual plasma EBV DNA after radiotherapy.

Inclusion Criteria:

1. Age ≥18 years;
2. Histologically confirmed nasopharyngeal carcinoma;
3. Expected survival time ≥12 weeks;
4. ECOG performance status: 0-1;
5. Received definitive radiotherapy (± induction and/or concurrent chemotherapy);
6. Plasma EBV DNA >0 copies/mL within the period from 1 week before to 4 weeks after completion of radiotherapy ;
7. Adequate organ function meeting the following criteria: Hematological: a. Hemoglobin (HB) ≥90 g/L; b. Absolute neutrophil count (ANC) ≥1.0×10⁹/L; c. Platelet count (PLT) ≥80×10⁹/L; Biochemical: a. Total bilirubin (BIL) <1.5× upper limit of normal (ULN); b. ALT and AST <2.5×ULN; c. Serum creatinine (Cr) ≤ULN, and creatinine clearance rate ≥50 mL/min (calculated by Cockcroft-Gault formula); d. Normal myocardial enzymes and thyroid function; e. Normal cardiac function assessed by echocardiography.
8. Signed informed consent with willingness to comply with the study protocol.

Exclusion Criteria:

1. Histologically confirmed keratinizing squamous cell carcinoma (WHO I)；

2. Distant metastasis detected by pre-treatment clinical or imaging examinations;

3. History of allergy to any component of monoclonal antibodies, tislelizumab, or capecitabine;

4. History of autoimmune diseases, except for the following conditions (eligible after evaluation):

   1. Autoimmune-related hypothyroidism on stable thyroid hormone replacement therapy;
   2. Type I diabetes mellitus under stable insulin therapy with controlled blood glucose;

5. Previous or concurrent malignancies (except those cured and disease-free for >5 years, e.g., basal cell carcinoma, cervical carcinoma in situ);

6. Positive pregnancy test in women of childbearing potential;

7. Concurrent medical conditions that may compromise patient enrollment or safety during the study;

8. History of idiopathic pulmonary fibrosis, drug-induced pneumonitis, organizing pneumonia, idiopathic pneumonia, or other active pulmonary diseases;

9. Active psychiatric disorders or other mental conditions affecting informed consent comprehension;

10. Uncontrolled active infections, including tuberculosis, hepatitis B (HBsAg+), hepatitis C, or HIV (HIV antibody+);

11. Significant cardiovascular diseases: NYHA Class II or higher, myocardial infarction within 1 year, unstable angina, or supraventricular/ventricular arrhythmias requiring clinical intervention;

12. Factors affecting drug administration, distribution, metabolism, or excretion (e.g., psychiatric/neurological disorders, chronic diarrhea, ascites, pleural effusion);

13. Unwillingness to sign informed consent.