Combination Chemotherapy in Treating Patients With Colorectal Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed colorectal cancer * Unresectable metastatic or locoregional disease * At least 1 measurable lesion outside a previously irradiated area or an area treated with physical devices (e.g., cryotherapy, laser, or thermoablation) * No prior enrollment in EORTC-05963 * No symptomatic brain metastases PATIENT CHARACTERISTICS: Age: * Over 18 Performance status: * WHO 0-2 Life expectancy: * Not specified Hematopoietic: * Neutrophil count greater than 2,000/mm\^3 * Platelet count at least 90,000/mm\^3 Hepatic: * Bilirubin no greater than 2 times upper limit of normal (ULN) Renal: * Creatinine no greater than 1.5 times ULN * No uncontrolled hypercalcemia Cardiovascular: * No overt cardiac disease Pulmonary: * No severe respiratory illness Other: * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Male patients must use effective barrier contraception during and for up to 6 months after study * No baseline diarrhea greater than grade I (must have less than 4 stools per 24 hours) * No prior grade III or IV toxicity related to irinotecan * No sensory or motor neuropathy with functional impairment * No prior hypersensitivity to any study drug * No other primary tumor except basal cell skin cancer or carcinoma in situ of the cervix * No uncontrolled infectious or chronic disease * No psychological, familial, sociological, or geographical condition that would preclude study PRIOR CONCURRENT THERAPY: Biologic therapy: * No concurrent prophylactic growth factor therapy Chemotherapy: * At least 1 month since prior chemotherapy * No prior irinotecan, fluorouracil, leucovorin calcium, and oxaliplatin as combination therapy * Other prior therapy containing irinotecan and/or oxaliplatin allowed * No more than 1 prior chemotherapy regimen for metastatic or locoregional disease * Adjuvant chemotherapy considered first-line therapy if tumor relapsed within 6 months of completion of therapy Endocrine therapy: * No concurrent corticosteroids except for emergencies Radiotherapy: * See Disease Characteristics * Palliative radiotherapy for bone lesion allowed except for disease progression Surgery: * See Disease Characteristics