The purpose of this study is to compare OnDose® based pharmacokinetic administration of 5-FU versus standard Body Surface Area (BSA) based administration of 5-FU in patients with metastatic colorectal cancer treated with mFOLFOX6, with or without bevacizumab, to determine if the use of OnDose® achieves an improvement in the Overall Response Rate (ORR) relative to BSA dosing response.