Combination Chemotherapy as First-Line Therapy in Treating Older Patients With Metastatic Colorectal Cancer That Cannot Be Removed By Surgery

DISEASE CHARACTERISTICS: * Histologically confirmed adenocarcinoma of the colon or rectum * Metastatic disease * Unresectable disease * Measurable disease that is outside the field of prior irradiation * No brain metastases PATIENT CHARACTERISTICS: * Karnofsky performance status 60-100% * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Transaminases ≤ 5 times normal * Bilirubin ≤ 1.5 times normal * Alkaline phosphatase \< 3 times normal (5 times normal if due to hepatic involvement) * Creatinine clearance \> 45 mL/min * Life expectancy \> 3 months * No psychological, social, or geographical situation that would preclude study treatment * No chronic diarrhea or enteropathy * No coronary insufficiency or symptomatic cardiac disease * No other malignancy unless curatively treated * No contraindication to chemotherapy PRIOR CONCURRENT THERAPY: * At least 6 months since prior adjuvant chemotherapy for the primary tumor * No prior extensive resection * No other concurrent anticancer therapy