Comparison of Combination Chemotherapy Regimens in Treating Patients With Metastatic Colorectal Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed colorectal carcinoma * Metastatic disease * Not amenable to surgery * Unidimensionally measurable disease * No bone metastases * No brain metastases PATIENT CHARACTERISTICS: Age * 18 to 75 Performance status * WHO 0-2 Life expectancy * At least 12 weeks Hematopoietic * Neutrophil count at least 2,000/mm\^3 * Platelet count at least 100,000/mm\^3 * Hemoglobin at least 10 g/dL Hepatic * Bilirubin no greater than 1.25 times upper limit of normal (ULN) (1.5 times ULN if hepatic metastases are present) * SGPT and SGOT no greater than 3 times ULN (5 times ULN if hepatic metastases are present) Renal * Creatinine no greater than 1.25 times ULN Cardiac * No concurrent cardiac abnormalities that would preclude study therapy Pulmonary * No concurrent pulmonary abnormalities that would preclude study therapy Other * Not pregnant or nursing * Fertile patients must use effective contraception * No chronic enteropathy * No other prior cancer within the past 5 years except carcinoma in situ of the cervix or curatively treated basal cell skin cancer * No concurrent severe uncontrolled infection * No obstruction or partial obstruction that would interfere with study therapy * No psychological, social, familial, or geographical situation that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent anticancer biological response modifiers Chemotherapy * No prior chemotherapy (except adjuvant chemotherapy completed more than 6 months ago) * No prior irinotecan * No prior oxaliplatin * No other concurrent chemotherapy Endocrine therapy * No concurrent anticancer hormonal therapy Radiotherapy * At least 4 weeks since prior pelvic radiotherapy * No prior abdominopelvic radiotherapy Surgery * At least 4 weeks since prior surgery * No prior extensive intestinal resection (i.e., more than 1 prior hemicolectomy or extensive resection of the small intestines) Other * No other concurrent experimental medication * No other concurrent anticancer therapy