This is a randomized phase II trial comparing the first-line treatment with nab-paclitaxel plus S-1(AS) and nab-paclitaxel plus gemcitabine(AG) in advanced pancreatic ductal adenocarcinoma (PDA) with primary tumor nonexcision in Chinese patients.

Advanced pancreatic ductal adenocarcinoma (PDAC) is an aggressive and chemo-resistant disease with extremely low 5-year survival rate. Gemcitabine has been the cornerstone of metastatic PDAC treatment for more than a decade , although survival benefit was very poor. Nab-paclitaxel added to gemcitabine has showed improving survival and overall response rate vs gemcitabine alone in metastatic PDAC first-line treatment in the MPACT phaseIII study, which represents one of the standards of care in advanced PDAC therapy. S-1 is an oral 5-fluorouracil (5-FU) prodrug, and shown to be non-inferior to gemcitabine on OS for unresectable pancreatic cancer. Meanwhile, adjuvant chemotherapy with S-1 monotherapy was found to significant prolong survival of pancreatic cancer patients when compared with gemcitabine. This study is to explore the efficacy and safety of nab-paclitaxel plus S-1(AS) and nab-paclitaxel plus gemcitabine(AG) as first-line treatment in advanced pancreatic ductal adenocarcinoma (PDA) with primary tumor nonexcision in Chinese patients.

Inclusion Criteria:

1. Signed informed-consent form.
2. Age no less than 18 years.
3. Histologically confirmed locally advanced or metastatic pancreatic ductal adenocarcinoma, with RECIST measurable lesions.
4. Eastern Cooperative Oncology Group (ECOG) 0-1 with life expectation of no less than 12 weeks.
5. Patients must have received no previous chemotherapy or investigational therapy for the treatment of locally advanced or metastatic disease.
6. At least 4 weeks since completion of the last operation except for diagnostic biopsy.
7. At least 4 weeks since completion of radiotherapy to lesions.
8. Not suitable for local treatment.
9. Adequate liver/bone marrow function.
10. Human Chorionic Gonadotropin (HCG) test negative for female with contraception measure until 3 months after study end.
11. Compliant, and can be followed up regularly.

Exclusion Criteria:

1. Received chemotherapy or investigational therapy for the treatment of locally advanced or metastatic disease.
2. Pregnant or breast-feeding female, or not willing to take contraception measures during study.
3. Serious infection requiring antibiotics intervention during recruitment.
4. Allergic to study drug.
5. More than grade 1 neuropathy.
6. Uncontrolled brain metastasis or mental illness.
7. Congestive heart failure, uncontrolled cardiac arrhythmia, etc.
8. Other malignancy within 5 years.
9. Can't be followed up or obey protocol.
10. Ineligible by the discretion of the investigator.