RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Bevacizumab may stop the growth of colorectal cancer by stopping blood flow to the tumor.

PURPOSE: Phase II trial to study the effectiveness of combination chemotherapy plus bevacizumab in treating patients who have advanced colorectal cancer.

OBJECTIVES: I. Determine the progression-free survival at 7 months of patients with previously untreated advanced colorectal cancer treated with fluorouracil, leucovorin calcium, irinotecan, and bevacizumab. II. Determine the response rate and overall survival of this patient population treated with this regimen. III. Determine the toxicity of this treatment regimen in these patients.

OUTLINE: This is a multicenter study. Patients receive irinotecan IV over 90 minutes, leucovorin calcium IV, and fluorouracil IV once weekly for 4 weeks. Patients also receive bevacizumab IV over 30-90 minutes once every 2 weeks. Treatment repeats every 6 weeks in the absence of disease progression or unacceptable toxicity. Patients are followed every 3 months for 2 years, every 6 months for 3 years, and then annually thereafter.

PROJECTED ACCRUAL: A total of 75 patients will be accrued for this study within 1 year.

DISEASE CHARACTERISTICS: Histologically confirmed advanced or metastatic adenocarcinoma of the colon and rectum Surgically unresectable disease Measurable disease Disease outside the prior radiotherapy port and/or progressive disease within the previously irradiated volume

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: Not specified Hematopoietic: WBC at least 3,000/mm3 Platelet count at least 100,000/mm3 No hemorrhagic events within the past 6 months Hepatic: Bilirubin normal SGOT normal INR no greater than 1.5 Renal: Creatinine no greater than 1.5 times upper limit of normal Cardiovascular: No thromboembolic events within the past 6 months Pulmonary: No evidence of pneumonia Other: No known hypersensitivity to recombinant humanized murine monoclonal antibodies No evidence of significant active infection (e.g., peritonitis or wound abscess) Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent sargramostim (GM-CSF) Chemotherapy: At least 12 months since prior fluorouracil-based adjuvant chemotherapy No prior adjuvant irinotecan Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics At least 2 weeks since prior radiotherapy and recovered Surgery: See Disease Characteristics Other: No prior therapy for advanced disease No concurrent therapeutic anticoagulation except for low-dose coumadin for maintenance of indwelling catheters