HCT116 cells were plated in 24 well plates at a density of 25,000 cells/well. Cells were transfected 12 h later with 100 nM NTC siRNA, 50 nM PIK3CA siRNA + 50 nM NTC siRNA, 50 nM KRAS siRNA + 50 nM NTC siRNA, or 50 nM PIK3CA siRNA + 50 nM KRAS siRNA. Media was exchanged 4 h later for either control media containing DMSO only, or media containing 1, 5, or 10 uM of 5-FU. Media was again exchanged for fresh drug media at 36 h post transfection. Proliferation was assessed by cell counting at 72 h (* p < 0.05 vs. control; † p < 0.05 vs. PIK3CA siRNA or KRAS siRNA alone).