Based on Western data, levels of 5-FU are highly variable when doses are based on BSA. A relationship between systemic plasma levels of 5-FU and treatment toxicity and efficacy exists. Whilst pharmacokinetically-guided dose management has been shown to improve 5-FU efficacy and tolerance, there is currently no data in Asian patients using this approach. Using pharmacokinetically guided 5-FU-dose adjustment, the investigators hypothesize the proportion of Asian patients achieving a target AUC of 20-24 mg.h/L is similar to that of Caucasians.