This single arm study will assess the efficacy and safety of a combination of modified FOLFIRI (irinotecan, 5-FU and leucovirin), Avastin and cetuximab in patients with previously untreated metastatic colorectal cancer. Patients will receive modified FOLFIRI (irinotecan 180mg/m2 iv, leucovirin 200mg/m2 iv, and 5-FU 400mg/m2 iv) on day 1 of each 2 week cycle, in combination with Avastin (5mg/kg iv on day 1 of each cycle) and cetuximab (loading dose of 400mg/m2 followed by 250mg/m2 on day 3 of each cycle). The anticipated time on study treatment is until disease progression or unacceptable toxicity, and the target sample size is <100 individuals.