PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent immunotherapy Concurrent filgrastim or epoetin alfa allowed Chemotherapy: At least one year since prior adjuvant systemic fluorouracil with or without levamisole or leucovorin No prior systemic or hepatic artery infusion chemotherapy for metastatic disease No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: No prior radiotherapy to the liver At least one year since radiotherapy to greater than 25% of bone marrow No concurrent radiotherapy Surgery: At least 21 days since abdominal exploration with or without intestinal resection Other: Oral cryotherapy allowed only on day 2 of each course