Peripheral blood was prospectively, anonymously sampled for each patient on the first day of the first cycle at 0 h (pre-dose) and 0.5, 1, 2, 4, 8, 24 h post-S-1/LV morning dosing. The 2 ml plasma at 0 h was separated for measuring baseline protein expression level of DPD, OPRT, TS, and TP. The 4-ml blood cells at 0 h were separated for CYP2A6 gene polymorphism. The 2 ml plasma at 0, 0.5, 1, 2, 4, 8, 24 h was separated for plasma concentrations of 5-FU.