Combination of Anti-PD-1 Antibody and Chemotherapy in Metastatic Pancreatic Cancer

Inclusion Criteria: * •Pathologically (histologically or cytologically) confirmed pancreatic ductal adenocarcinoma (PDAC). * Recurrent disease or metastatic disease (such as liver, peritoneum, lung) evaluated by abdominal contrast-enhanced CT, MRI, and chest CT. PET/CT or other imaging examinations would be used if necessary. * Never receive any systematic treatment or Progression after fisrt line Gemcitabine base chemotherapy * ECOG score 0 or 1. * Serum creatinine level is normal, and serum total bilirubin level is less than 1.5 x ULN. * ALT and AST are less than 2 x ULN. * Signed informed consent. Exclusion Criteria: * •History of participation of other clinical trails within 4 weeks * History of autoimmune disease or other condition receiving glucocorticoid treatment * History of receiving chemotherapy within 2 weeks * History of radiotherapy and molecular target therapy within 2 weeks * History if active tuberculosis * History of malignance treatment in the past, excluding basal and cutaneous squamous cell carcinoma, cervical carcinoma in situ, papillary thyroid carcinoma * Major cardiovascular diseases (including myocardial infarction, unstable angina, congestive heart failure, severe uncontrolled arrhythmia) during the past six months of enrollment. * Hematological precancerous diseases, such as myelodysplastic syndromes. * Evidence of clinical-related or previous interstitial lung disease, such as noninfectious pneumonia or pulmonary fibrosis, or baseline chest CT scan or chest X-ray findings * Previous or physical findings of central nervous system disease, except for adequately treated (e.g. primary brain tumors, uncontrolled seizures or strokes with standard medications) * Preexisting neuropathy \> 1 (NCI CTCAE). * Immune deficiency syndrome, such as active tuberculosis and HIV infection. * Allograft requires immunosuppressive therapy or other major immunosuppressive therapies. * Severe serious wounds, ulcers or fractures. * Clinical evaluation is unacceptable