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.