Combination of Radiation Therapy and Anti-PD-1 Antibody in Treating Patients With Pancreatic Cancer

Inclusion Criteria: 1. age:18-75 years, male or female. 2. Histologically or cytologically confirmed pancreatic cancer. 3. Measurable disease based on Response Evaluation Criteria In Solid Tumors (RECIST) 1.1. 4. Can provide either a newly obtained or archival tumor tissue sample. 5. ECOG 0-1. 6. Life expectancy of greater than 12 weeks. 7. Adequate organ function. 8. Patient has given written informed consent. Exclusion Criteria: 1. Patients who have or are currently undergoing additional chemotherapy, radiation therapy, targeted therapy or immunotherapy. 2. Other malignancy within 5 years prior to entry into the study, expect for curatively treated basal cell and squamous cell carcinoma of the skin and/or curatively resected in-situ cervical and/or breast cancers. 3. Known central nervous system (CNS) metastases. 4. Subjects with any active autoimmune disease or history of autoimmune disease. 5. Uncontrolled clinically significant heart disease, including but not limited to the following: (1) \> NYHA II congestive heart failure; (2) unstable angina, (3) myocardial infarction within the past 1 year; (4) clinically significant supraventricular arrhythmia or ventricular arrhythmia requirement for treatment or intervention; 6. Active infection or an unexplained fever \> 38.5°C during screening or before the first scheduled day of dosing (subjects with tumor fever may be enrolled at the discretion of the investigator); 7. History of Interstitial Pneumonia or active non-infectious pneumonitis. 8. Known Human Immunodeficiency Virus (HIV) infection、active Hepatitis B or Hepatitis C. 9. Prior therapy with a PD-1, anti-PD-Ligand 1 (PD-L1) agent. 10. Concurrent medical condition requiring the use of cortisol (\>10mg/day Prednisone or equivalent dose) or other systematic immunosuppressive medications within 14 days before the study treatment. Except: inhalation or topical corticosteroids. Doses \> 10 mg/day prednisone or equivalent for replacement therapy. 11. Has received prior anti-cancer monoclonal antibody (mAb), chemotherapy, targeted small molecule therapy, or radiation therapy within 4 weeks prior to study Day 1 or not recovered from adverse events due to a previously administered agent. 12. Received a live vaccine within 4 weeks of the first dose of study medication. 13. Pregnancy or breast feeding. Decision of unsuitableness by principal investigator or physician-in-charge.