Study Comparing Optimized 5-FU Dosing and Standard Dosing in Metastatic Colorectal Cancer Patients Treated With mFOLFOX6

Selection Criteria: * Patients with histologically confirmed metastatic colorectal cancer * No prior chemotherapy for the treatment of metastatic colorectal cancer * At least one measurable lesion by CT or MRI of ≥ 20 mm (if conventional CT scan) or ≥ 10 mm (if spiral CT scan) * ECOG Performance Status (ECOG-PS) status ≤ 2 * At least 18 years of age * Life expectancy \> 6 months * Must be able and willing to give written informed consent * Women of child-bearing potential (i.e., women who are pre-menopausal or not surgically sterile) must use acceptable contraceptive methods (abstinence, intrauterine device \[IUD\], oral contraceptive or double barrier device), and must have a negative serum or urine pregnancy test within 1 week prior to beginning treatment on this trial. Nursing patients are excluded. Sexually active men must also use acceptable contraceptive methods (abstinence, condom). * ANC count greater than or equal to 1,500/ mm³ * Platelets greater than or equal to 100,000/ mm³ * Serum creatinine less than or equal to 2x upper limit of normal (normal range (male): 97-137 mL/min; (female): 88-128 mL/min) * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) less than or equal to 3x the upper limit of normal (≤ 5.0 x ULN is acceptable if liver has tumor involvement) (ALT normal range: \< 41 iu/L (male), \< 31 iu/L (female); AST normal range: \< 37 iu/L (male), \< 31 iu/L (female)). * Prothrombin Time (PT), activated partial thromboplastin time (aPTT) and INR ≤ 1.5 x ULN (INR normal range: 0.8-1.2) or in the therapeutic range if on anticoagulation. * Hemoglobin greater than or equal to 9 gm/dl (may be corrected by transfusion prior to 5-FU treatment with investigator approval).