Capecitabine Plus Toripalimab Maintenance Therapy in Metastatic Nasopharyngeal Carcinoma After First-line Treatment

Inclusion Criteria: 1. Histology confirmed metastatic nasopharyngeal carcinoma following radical treatment（Stage IVb, AJCC/UICC 8th，any T，any N，M1） 2. Patients receiving gemcitabine/cisplatin in combination with terriprizumab received complete response (CR) or partial response (PR) after 4-6 cycles of imaging studies 3. Age ≥18 years and ≤65 years 4. WBC≥4×10\^9/L, platelet ≥ 100×10\^9/L, hemoglobin ≥ 90g/L and Albumin≥28 g/L 5. With normal liver function test (TBIL#ALT#AST ≤ 2.5×uln) (patients with liver metastasis≤5×uln) 6. With normal renal function test (creatinine ≤ 1.5×uln or CCR ≥ 60ml/min) 7. ECOG score is 0-1 8. At least one measurable lesion according to RECIST v 1.1 (prior to gemcitabine/cisplatin plus toripalimab) 9. Life expectancy is at least 12 weeks 10. Patients sign informed consent forms Exclusion Criteria: 1. History of severe anaphylaxis to any component of capecitabine or toripalimab 2. Active or untreated central nervous system metastases 3. Patient with necrotic lesions and judged by the investigator to be at risk of excessive bleeding 4. Patients with poorly controlled pleural effusion, pericardial effusion, or ascites requiring frequent drainage. Patients with indwelled catheters are allowed to participate. 5. Patients with poorly controlled or symptomatic hypercalcemia 6. Pregnancy or lactation 7. Malignancies other than nasopharyngeal carcinoma, with negligible risk of metastasis or death and radical outcome expected after treatment, within the 5 years prior to enrollment. 8. Patients who have previously received allogeneic bone marrow transplants or solid organ transplants. 9. History of autoimmune diseases 10. Received systemic immunostimulant therapy (except toripalimab in palliative chemotherapy, including but not limited to interferon or IL-2) within 4 weeks prior to enrollment or during 5 half-lives of the drug. 11. Receive any active vaccine within 4 weeks prior to enrollment 12. Basic medical conditions that the investigator identified as likely to affect significantly drug administration and protocol adherence of the study 13. Active pneumonia 14. Active infections, including tuberculosis, hepatitis B, hepatitis C or HIV. 15. Presence of severe neurological or psychiatric disorders, including dementia and seizures. 16. Peripheral nerves which was graded as≥ 2 according to NCI-CTCAE 17. Major cardiovascular diseases