5-FU 2400 mg/m2 by continuous intravenous infusion over 46 hours (may be delivered via automated outpatient pump) Antiemetics: 5-HT3 receptor antagonist (e.g. ondansetron) and dexamethasone are recommended prior to chemotherapy Placebo by intravenous infusion over 60 minutes every week (participants larger than 100 kg [220 pounds] will receive their infusions over 120 minutes).