Comparing Two Combination Chemotherapy Regimens in Treating Patients With Metastatic Colorectal Cancer

DISEASE CHARACTERISTICS: Histologically confirmed unresectable metastatic adenocarcinoma of the colon or rectum Bidimensionally measurable or evaluable disease outside previously irradiated area No bone metastasis as target lesion At least 1 cm if spiral CT scan OR At least 2 cm if conventional CT scan No CNS metastasis No symptomatic ascites or pleural effusion that is not evacuated No total or partial bowel obstruction PATIENT CHARACTERISTICS: Age: 18 to 80 Performance status: ECOG 0-2 WHO 0-2 Life expectancy: Not specified Hematopoietic: Neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Alkaline phosphatase less than 5 times upper limit of normal (ULN) Renal: Creatinine less than 3 times ULN No uncontrolled hypercalcemia Cardiovascular: No uncontrolled congestive heart failure, angina pectoris, hypertension, or arrhythmias Other: No peripheral sensory neuropathy No prior significant neurologic or psychiatric disorders No other malignancy within past 5 years except adequately treated carcinoma in situ of the cervix or basal or squamous cell skin carcinoma No active infection No other concurrent serious disease Not pregnant or nursing Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: No prior immunotherapy for metastatic disease Chemotherapy: Prior adjuvant chemotherapy allowed, provided progression-free interval of more than 6 months since end of last course No prior oxaliplatin or irinotecan No prior chemotherapy for metastatic disease No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics No concurrent radiotherapy Surgery: Concurrent surgery allowed Other: At least 30 days since other prior investigational drugs No other concurrent investigational treatment No other concurrent antitumoral treatment