Second-Line Adjuvant Therapy With Nab-Paclitaxel Plus Gemcitabine Versus Oxaliplatin Plus Folinic Acid and Fluorouracil for Gemcitabine-Refractory Pancreatic Cancer After Curative Resection

PRIMARY OBJECTIVES: * To evaluate the therapeutic efficacy of second-line adjuvant therapy with nab-paclitaxel plus gemcitabine (AG) versus oxaliplatin plus folinic acid and fluorouracil (OFF) in terms of overall survival for gemcitabine-refractory pancreatic cancer after curative resection. SECONDARY OBJECTIVES: * To evaluate the therapeutic efficacy of two regimens in terms of objective response rate according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 * To evaluate the time to remission of patients treated with the two regimens. * To evaluate the progression-free survival of patients treated with the two regimens. * To evaluate the levels of tumor biomarkers in serum of patients treated with the two regimens, including Carbohydrate Antigen (CA)19-9、CA125、CA153、CA242、CA72-4、CA50、CEA、AFP. * To evaluate the occurrence of grade 3 and 4 toxicities according to National Cancer Institute Common Toxicity Criteria for Adverse Effects (NCI CTCAE) version 4.0 in patients treated with the two regimens. * To evaluate the quality of life score of patients treated with the two regimens. Detailed Description of Arms: Patients are randomized to 1 of 2 treatment arms (Arm AG or Arm OFF). Arm AG: Firstly, patients 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. Secondly, patients 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 until there is disease progression or recurrence. Arm OFF: Patients receive oxaliplatin 85 mg/m\^2 (iv, 2 hours) on days 8 and 22 with 42 days as a cycle. Patients receive folinic acid 200 mg/m\^2 (iv) and fluorouracil 2000 mg/m\^2 (iv, 24 hours) on days 1, 8, 15 and 22 for 4 weeks, followed by 2 weeks without treatment. Oxaliplatin is given before folinic acid and fluorouracil when the three drugs are given on the same days. Treatment repeats until there is disease progression or recurrence.