Incidences of de novo metastatic nasopharyngeal carcinoma range from 6% to 8% at the time of presentation. For the initial diagnosis of metastatic NPC, PD-1 plus chemotherapy yields a satisfactory outcome with1year PFS of 40%. Previous study demonstrated the benefit of adding radiotherapy to chemotherapy in metastatic NPC, however there is no evidence whether radiotherapy can further improve PFS based on chemotherapy plus PD-1 . The purpose of this study is to evaluate the safety and effectiveness of first-line immunochemotherapy combined with radiotherapy for initial diagnosed metastatic NPC.

Inclusion Criteria:

• Age:18-75 years, male or female.
• ECOG 0-2
• Histologically or cytologically confirmed de novo metastatic nasopharyngeal carcinoma.(stage IVb, AJCC 8th)
• Complete response or partial response after at least 3 cycles (no more than 6 cycles) of chemotherapy combined with immunotherapy
• Measurable disease based on Response Evaluation Criteria In Solid Tumors (RECIST) 1.1.
• Adequate organ function.
• Patient has given written informed consent.

Exclusion Criteria:

• Unwilling or unable to provide informed consent
• Intolerance to radiotherapy or immunotherapy
• Patients who have head and neck radiotherapy history.
• previous or recent another malignancy, except for nonmelanoma skin cancer or cervical cancer in situ
• women in pregnancy, lactation period, or no pregnancy test 14 days before the first dose
• in other clinical trials within 30 days
• Patients with autoimmune disorder, including but not limited to systemic lupus erythematosus or multiple sclerosis;
• History of primary immunodeficiency
• History of active tuberculosis, drug-induced interstitial lung disease, or ≥ Grade 2 pulmonitis;
• Patients with human immunodeficiency virus (HIV) positive;
• Comorbidities that cannot be controlled by concomitant treatment, including but not limited to: ongoing or active infection, unexplained fever > 38.5°C (subjects with neoplastic fever are judged by the investigator to be included), symptomatic congestive heart failure ≥ Grade 2 according to New York Heart Association (NYHA) functional classification, LVEF (left ventricular ejection fraction) < 50%, hypertension poorly controlled by drugs, unstable angina, arrhythmia, active peptic ulcer disease or gastritis;
• not suitable for this study judged by researchers