A Study Evaluating the Efficacy and Safety of MEGF0444A Dosed to Progression in Combination With Bevacizumab and mFOLFOX-6 in Participants With Previously Untreated Metastatic Colorectal Cancer

Participants will receive 5-fluorouracil 400 milligrams per squared meter (mg/m\^2) intravenous (IV) bolus and then 2400 mg/m\^2 as a continuous IV infusion over 46-48 hours on Day 1 of every cycle until disease progression, unacceptable toxicity or at the maximum of 52 cycles, whichever occurs first.

Participants will be administered bevacizumab at a dose of 5 milligrams per kilogram (mg/kg) every 14 days until disease progression or unacceptable toxicity, for a maximum of 52 cycles, whichever occurs first.

Participants will receive folinic acid 400 mg/m\^2 IV infusion over 2 hours on Day 1 of every cycle until disease progression, unacceptable toxicity or at the maximum of 52 cycles, whichever occurs first.

Participants will be administered MEGF0444A at a fixed dose of 400 milligrams (mg) IV on Day 1 of Cycle 1, followed by subsequent doses of 400 mg every 14 days until disease progression or unacceptable toxicity, for a maximum of 52 cycles, whichever occurs first.

Participants will receive oxaliplatin 85 mg/m\^2 IV infusion over 90 minutes on Day 1 of every cycle for a maximum of 8 cycles.

Participants will be administered MEGF0444A matching placebo every 14 days until disease progression, unacceptable toxicity or at the maximum of 52 cycles, whichever occurs first.