Inclusion Criteria:
* Diagnosed as metastatic NPC with no more than 5 metastatic lesions;
* Histopathological diagnosis of NPC;
* ECOG 0-1 point;
* Has not received prior systemic treatment, such as radiotherapy, chemotherapy, immunotherapy or biotherapy;
* No contraindications to immunotherapy and chemoradiotherapy;
* Every metastatic lesions could receive SBRT safely;
* Subject must have a measurable target lesion based on RECIST v1.1;
* Adequate marrow function: WBC count ≥ 3×10E9/L, NE count ≥ 1.5×10E9/L, HGB ≥ 90g/L, PLT count ≥ 100×10E9/L;
* Adequate liver function: ALT/AST ≤ 2.5×ULN, TBIL ≤ 2.0×ULN;
* Adequate renal function: BUN/CRE ≤ 1.5×ULN or endogenous creatinine clearance ≥ 60ml/min (Cockcroft-Gault formula);
* Take effective contraceptions during and three months after treatment;
* Patients must be informed of the investigational nature of this study and give written informed consent.
Exclusion Criteria:
* Allergic to monoclonal antibodies, any PD-1 antibody components, gemcitabine and cisplatin;
* Unexplained fever \> 38.5 ℃, except for tumor fever;
* Have active autoimmune disease (e.g., uveitis, enteritis, hepatitis, hypophysitis, nephritis, vasculitis, hyperthyroidism, and asthma requiring bronchodilator therapy);
* Have a known history of human immunodeficiency virus (HIV), active Hepatitis B (HBV-DNA ≥10E3copiers/ml) or hepatitis C virus (HCV) antibody positive;
* Have previously treated with PD-1 antibody or other immunotherapy for PD-1/PD-L1 pathway;
* Have New York Heart Association (NYHA) class 3 or 4, unstable angina, myocardial -infarction within 1 year, or clinically meaningful arrhythmia that requires treatment; Have known allergy to large molecule protein products or any compound of study therapy;
* Pregnant or breastfeeding;
* Prior malignancy except adequately treated non-melanoma skin cancer, in situ cervical cancer, and papillary thyroid carcinoma;
* Have received a live vaccine within 30 days of planned start of study therapy Has psychiatric drug or substance abuse disorders that would interfere with cooperation with the requirements of the trial;
* Any other condition, including mental illness or domestic/social factors, deemed by the investigator to be likely to interfere with a patient's ability to sign informed consent, cooperate and participate in the study, or interferes with the interpretation of the results.
