MiaPaCa-2 and Panc-1 cells (1,000 cells/well) were plated in 96-well extremely low attachment plates (Corning, Inc.) and treated with oxaliplatin (5 µM)/cisplatin (5 µM)/carboplatin (4 µM) at 37°C for 48 h. Fibroblast growth factor (20 ng/ml), human recombinant epidermal growth factor (20 ng/ml) and serum substitute B27 (1X) were mixed into serum-free DMEM/F-12 and were added to each well (all from Invitrogen; Thermo Fisher Scientific, Inc.). The number of spheres >50 mm in diameter was counted under a light microscope after 2 weeks of incubation at 37°C and 5% CO2.