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