A Study of Penpulimab and Anlotinib Plus Nab-paclitaxel and Gemcitabine for Metastatic Pancreatic Cancer.

Inclusion Criteria:

* Ages ≥18 years，ECOG ≤ 2，Estimated survival time \> 3 months
* Histologically or Cytologically confirmed metastatic pancreatic adenocarcinoma
* Based on Response Evaluation Criteria In Solid Tumors (RECIST1.1), there should be at least one measurable lesion
* Patients have never received systematical anti-cancer therapy
* Laboratory examination meets the following requirements:White blood cell (WBC) ≥3.0×109/L; absolute neutrophil count (ANC) ≥1.5×109/L; Hemoglobin (HB) ≥90g/L; platelet count(PLT) ≥75×109/L; Total bilirubin (TBIL) ≤1.5× normal upper limit (ULN); Alanine aminotransferase (ALT) and Aspartate aminotransferase (AST)≤2.5×ULN, if accompanied by liver metastasis, ALT and AST≤5×ULN; Serum creatinine (Cr) ≤1×ULN or creatinine clearance (CCr)≥50ml/min;
* Doppler ultrasound evaluation: left ventricular ejection fraction (LVEF) \> 50%
* Patients of childbearing age should take appropriate protective measures before enrollment and during the trial
* Volunteer to join the study, sign the informed consent, have good compliance, and cooperate with follow-up
* Ability to follow the study protocol and follow-up procedures.

Exclusion Criteria:

* Patients have ever received any systematical anti-cancer therapy in the past
* Patients who participated in other clinical trials in the past 4 weeks
* According to the investigator, patients who surgically available or potentially treatable(Patients who voluntarily give up surgical treatment can be enrolled after evaluation by the investigator)
* Patients with moderate ascites requiring drainage
* Patients with CNS metastases and/or carcinomatous meningitis
* Patients with history of other primary malignancies except: 1) complete remission before enrollment for at least 2 years and requiring no additional treatment during the study period; 2) Adequately treated non-melanoma skin cancer or lentiform malignancy with no evidence of disease recurrence; 3) Adequately treated carcinoma in situ with no evidence of disease recurrence;
* Patients with autoimmune disease or immune deficiency who are treated with immunosuppressive drugs
* Patients with bleeding tendency.
* Pregnant or lactating women.
* Drug abuse, clinical or psychological or social factors that impact informed consent or the conduct of the study
* Patients who may be allergic to PD-1 monoclonal antibody, anlotinib, albumin-bound paclitaxel and gemcitabine