• Overall Response Rate [ Time Frame: through study completion, an average of 1 year ]
  To evaluate the Overall Response Rate of patients with metastatic pancreatic cancer after treated with nab-paclitaxel plus gemcitabine.
• Progression Free Survival [ Time Frame: through study completion, an average of 1 year ]
  To evaluate the Progression Free Survival of patients with metastatic pancreatic cancer after treated with nab-paclitaxel plus gemcitabine.

• overall survival [ Time Frame: through study completion, an average of 1 year ]
  To evaluate the overall survival of patients with metastatic pancreatic cancer after treated with nab-paclitaxel plus gemcitabine.
• adverse events [ Time Frame: through study completion, an average of 1 year ]
  adverse events of patients with metastatic pancreatic cancer after treated with nab-paclitaxel plus gemcitabine.

While GT (Gemcitabine + Nab-paclitaxel) is one of the preferred regimens for metastatic pancreatic cancer, we have yet to determine the optimum number of cycles for GT treatment regimen. In this single arm, open-label clinical trial, metastatic pancreatic cancer patients will be received nab-paclitaxel 100 mg/m^2 (iv, 30 minutes) and gemcitabine 1000 mg/m^2 for 3 weeks, followed by one week without treatment. Treatment repeats every 4 weeks until the disease recurrence or unacceptable toxicity, death or begin a novel therapeutic.

The safety and efficacy of each group will be assessed through ORR, PFS, OS and adverse effects as graded by CTC-AE 5.0.

• Drug: Paclitaxel for Injection（Albumin Bound）
  Patients firstly receive nab-paclitaxel 100 mg/m^2 (iv, 30 minutes) on days 1, 8, and 15 for 3 weeks, followed by one week without treatment. Treatment repeats every 4 weeks until the disease recurrence or unacceptable toxicity，death or begin a novel therapeutic.
  Other Name: Paclitaxel
• Drug: Gemcitabine
  Patients secondly receive gemcitabine 1000 mg/m^2 (iv, 30 minutes) on days 1, 8, and 15 for 3 weeks, followed by one week without treatment. Treatment repeats every 4 weeks until the disease recurrence or unacceptable toxicity，death or begin a novel therapeutic.

Inclusion Criteria:

1. Signed informed content obtained prior to treatment. The patients were fully explained and understood the purpose, contents, predicted efficacy, pharmacological effects, and risks of this study.

2. target population

   • the patients were confirmed as metastatic pancreatic cancer by histopathology or cytopathology.
   • At least one measurable objective lesion (both primary and metastatic) was identified based on the RECIST1.1 criteria;
   • Eastern Cooperative Oncology Group (ECOG) performance status 0-1;
   • The expected survival after surgery ≥ 3 months
   • The subjects have good compliance, can be treated and followed up, and voluntarily comply with the relevant provisions of this study
   • No contraindications for gemcitabine and nab-paclitaxel.

3. Age and reproductive status

   • Age ≥ 18 years and ≤ 75 years
   • Subjects of child-bearing age must agree to take effective contraceptive measures during the study period; Serum or urine pregnancy tests must be negative for women of childbearing age 24 hours before the start of chemotherapy;
   • Women must not lactate.

Exclusion Criteria:

1. The target disease has cerebral metastasis;

2. medical history and complications

   • patients had uncontrolled serious medical condition that the investigator considered may affect the subject's to receive treatment under the study program, For example, patients with severe medical diseases, including severe heart disease, cerebrovascular disease, uncontrolled diabetes, uncontrolled hypertension, uncontrolled infection, active peptic ulcer, etc.
   • Dementia, changing of mental state or any mental illness which could hinder understanding or informed consent or fill out questionnaires;
   • History of allergy or hypersensitivity to any therapeutic ingredient;
   • Combined with other malignant tumors excepted pancreatic cancer within the first 5 years of randomization, excepted well-treated basal cell or squamous cell carcinoma of the skin, localized prostate cancer after radical resection, and ductal carcinoma in situ of the breast after radical resection.
   • Previously received systemic therapy for advanced/metastatic pancreatic cancer;
   • Subjects who had previously been pathologically diagnosed with squamous cell carcinoma (no organ limitation) and received neoadjuvant/adjuvant therapy with taxa regimen.
   • Patients who had Grade 2 or above Peripheral neuropathy.

3. Abnormal results of physical examination and laboratory examination

   • Absolute neutrophil count (ANC) 90g/L 1.5 × 109/L; Platelets (PLT) 90g/L 100 × 109/L; Hemoglobin (Hgb) < 90g/L
   • Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase [SGOT]/ alanine aminotransferase (ALT) (serum glutamic pyruvate transaminase [SGPT]) >2.5 × institutional upper limit of normal (ULN), >5 × institutional upper limit of normal (ULN) (hepatic metastases); Total bilirubin (TBIL)>1.5 × ULN;
   • Creatinine (CRE)> 1.5 × ULN
   • Prothrombin time (PT) and international normalized ratio (INR) > 1.5 × ULN. Unless the subject had received anticoagulant treatment
4. Subjects had hepatitis b surface antigen (HBsAg)-positive and hbv-dna titer in peripheral blood greater than or equal to 1000 copy number /L;If HBsAg is positive and the peripheral blood hbv-dna <1000 copy number /L, the subjects will be eligible for inclusion if the investigator considers that chronic hepatitis b is stable and does not increase the risk of subjects.
5. Human immunodeficiency virus (HIV)- or hepatitis C virus (HCV) positive patients;
6. Patients combined with other anti-tumor drugs.
7. Participation in any trial drug treatment or another interventional clinical trial 30 days before screening period.
8. The researchers considered that there were other conditions that were not suitable for enrollment.