Fluorouracil, Leucovorin, and Irinotecan in Treating Patients With Recurrent or Refractory Metastatic Unresectable Colorectal Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed colorectal adenocarcinoma * Metastatic, unresectable disease * Meets 1 of the following criteria: * At least 1 unidimensionally measurable metastatic lesion at least 10 mm by spiral scan OR 20 mm by conventional scan * Evaluable disease * Evidence of disease (e.g., ascites or bone metastases) by imaging techniques * Progressive disease as defined by 1 of the following criteria: * Progressive disease while receiving first-line chemotherapy * Recurrent disease within 6 months after completing adjuvant chemotherapy * No symptomatic brain metastases PATIENT CHARACTERISTICS: Age * 18 to 80 Performance status * WHO 0-2 Life expectancy * At least 3 months Hematopoietic * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 Hepatic * Bilirubin \< 1.5 times upper limit of normal (ULN) * Alkaline phosphatase \< 3 times ULN Renal * Not specified Cardiovascular * No uncontrolled angina * No myocardial infarction within the past 6 months Gastrointestinal * No chronic diarrhea grade 2 or greater * No unresolved fully or partially obstructed intestine Other * Not pregnant or nursing * Fertile patients must use effective contraception * No other underlying disease or medical condition that would preclude study participation * No other prior malignancy except curatively treated basal cell cancer or carcinoma in situ of the cervix * No psychological, social, familial, or geographical condition that would preclude study follow-up PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * See Disease Characteristics * No prior irinotecan Endocrine therapy * Not specified Radiotherapy * At least 3 weeks since prior radiotherapy Surgery * At least 3 weeks since prior surgery Other * No other concurrent clinical trial participation