DISEASE CHARACTERISTICS: Histologically confirmed metastatic colorectal cancer At least 2 bidimensionally measurable lesions No CNS disease (e.g., primary brain tumor, seizures not controlled with standard therapy, or any brain metastases) No clinically detectable ascites

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-1 Life expectancy: More than 3 months Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 75,000/mm3 Hemoglobin at least 9 g/dL (may be transfused) No bleeding diathesis or coagulopathy Hepatic: AST or ALT no greater than 2.5 times upper limit of normal (ULN) (less than 5 times ULN if liver metastasis present) Bilirubin no greater than 1.6 mg/dL International normalized ratio less than 1.5 Renal: Creatinine no greater than 2.0 mg/dL No proteinuria or clinically significant impairment of renal function Cardiovascular: No clinically significant cardiovascular disease including uncontrolled hypertension, myocardial infarction, or unstable angina within past year No New York Heart Association class II-IV congestive heart failure within past year No serious cardiac arrhythmia requiring medication or grade II or greater peripheral vascular disease within past year Other: Must be able to tolerate CT scan contrast dye No other invasive malignancy within past 5 years except basal cell skin cancer No CNS disease including uncontrolled seizures or stroke No active infection requiring parenteral antibiotics No serious nonhealing wound, ulcer, or bone fracture No other disease or medical condition that would preclude study Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior biologic therapy for colorectal cancer Chemotherapy: At least 12 months since prior fluoropyrimidines with leucovorin and/or levamisole No other prior chemotherapy Endocrine therapy: Not specified Radiotherapy: At least 14 days since prior radiotherapy No prior radiotherapy to any indicator lesion Surgery: At least 28 days since prior surgical procedure At least 7 days since prior fine needle aspiration No concurrent major surgical procedure Other: At least 10 days since prior full-dose oral or parenteral anticoagulants except to maintain patency of pre-existing, permanent indwelling IV catheters At least 10 days since prior full-dose oral or parenteral thrombolytic agent At least 28 days since participation in other experimental drug study No chronic, daily aspirin or nonsteroidal anti-inflammatory medications No concurrent full-dose oral or parenteral anticoagulants (except for indwelling IV catheter maintenance) or thrombolytic agent