PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease Characteristics One and only 1 prior chemotherapy regimen for metastatic disease consisting of first-line irinotecan, fluorouracil, and leucovorin calcium (Saltz regimen) Prior adjuvant fluorouracil with leucovorin calcium allowed At least 3 weeks since prior chemotherapy for metastatic disease and recovered No prior adjuvant irinotecan No prior oxaliplatin Endocrine therapy: Not specified Radiotherapy: No prior radiotherapy to study lesions unless evidence of progressive disease within the radiotherapy port At least 3 weeks since prior radiotherapy Surgery: See Disease Characteristics At least 4 weeks since prior major surgery and recovered Prior surgical resection of primary tumor or metastases allowed Other: At least 30 days since prior investigational drugs No other concurrent investigational agents No other concurrent anti-cancer therapy No concurrent participation in other investigational trials