This is a prospective, single-arm, phase II clinical trial. The purpose of this study is to evaluate the efficacy and adverse effect of SBRT and LDRT combined with programmed death 1 (PD-1) antibody and chemotherapy in recurrent/metastatic nasopharyngeal carcinoma patients.

Inclusion Criteria:

• Diagnosed as recurrence/metastatic NPC
• Histopathological diagnosis of NPC(WHO II/III)
• ECOG 0-1 point
• No treatment to r/mNPC, such as radiotherapy, chemotherapy, immunotherapy or biotherapy;
• No contraindications to immunotherapy and chemoradiotherapy;
• At least one lesion 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 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.