Bevacizumab and Combination Chemotherapy as First-Line Therapy in Treating Patients With Metastatic Colorectal Cancer That Cannot Be Removed by Surgery

DISEASE CHARACTERISTICS: * Histologically confirmed adenocarcinoma of the colon or rectum * No other histological types * Metastatic, unresectable disease * No bone metastases only * Unidimensionally measurable metastatic disease * No CNS metastases PATIENT CHARACTERISTICS: * WHO performance status (PS) 0-2 OR Karnofsky PS 70-100% * Life expectancy ≥ 12 weeks * ANC \> 1,500/mm³ * Platelet count ≥ 100,000/mm³ * Hemoglobin ≥ 10 g/dL * Bilirubin ≤ 1.25 times normal (1.5 times normal in presence of hepatic metastases) * AST and ALT \< 3 times normal (5 times normal in presence of hepatic metastases) * Creatinine \< 1.25 times normal * No proteinuria * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * No other cancer in the past 5 years except for carcinoma in situ of the uterine cervix or basal cell skin cancer * No hypersensitivity to fluorouracil * No hypersensitivity to leucovorin calcium, bevacizumab, or their excipients * No hypersensitivity to Chinese hamster ovarian cell products or other recombinant humanized or nonhumanized monoclonal antibodies * No allergy to irinotecan hydrochloride * No prior reaction to attenuated vaccines (fever, jaundice) * No poor nutritional status * No Biermer anemia or other anemia due to vitamin B12 deficiency * No uncontrolled symptomatic occlusion or subocclusion * No medullary hypoplasia or severe insufficiency * No prior chronic intestinal disease * No Gilbert's syndrome * No intra-abdominal inflammatory reaction (e.g., gastroduodenal ulcer, diverticulitis, or colitis) * No chronic intestinal inflammatory disease * No thromboembolic arterial condition in the past 6 months, including any of the following: * Cardiovascular accident * Transient ischemic attack * Myocardial infarction * No infection or serious noncancerous disease * No condition that is unstable or would increase risk to the patient, including any of the following: * Unstable angina * Poorly controlled hypertension * Severe cardiac insufficiency * Serious arrhythmia * Bleeding diathesis * Pulmonary disease at risk of decompensation * No familial, geographical, social, or psychological condition that would preclude study participation * No prisoners or patients without guardians PRIOR CONCURRENT THERAPY: * At least 8 weeks since prior surgery * At least 6 months since prior adjuvant chemotherapy * At least 1 month since prior palliative chemotherapy * No prior abdominal or pelvic radiotherapy * At least 30 days since prior participation in another investigational study * No prior bevacizumab * No extensive intestinal resection (e.g., partial colectomy or extensive thin resection) * No concurrent warfarin, Hypericum perforatum (St. John's wort), or prophylactic phenytoin