Irinotecan, Fluorouracil, and Leucovorin in Treating Patients With Advanced Gastrointestinal Cancer

DISEASE CHARACTERISTICS: * Biopsy confirmed diagnosis of gastrointestinal cancer * Advanced, unresectable disease * Confirmation of UGT1A1 TA indel genotype * Measurable or evaluable (non-measurable) disease * Measurable disease is defined as ≥ 1 lesion that can be accurately measured (longest diameter to be recorded) as ≥ 2.0 cm with conventional techniques or as ≥ 1.0 cm with spiral CT scan * Clinical lesions will only be considered measurable when they are superficial (e.g., skin nodules, palpable lymph nodes) * Lesions on chest x-ray are acceptable as measurable lesions when they are clearly defined and surrounded by aerated lung * The following are considered non-measurable disease: * Bone lesions * Leptomeningeal disease * Ascites * Pleural/pericardial effusions * Lymphangitis cutis/ pulmonis * Inflammatory breast disease * Abdominal masses (not followed by CR scan or MRI) * Cystic lesions * All other lesions (or sites of disease), including small lesions (longest diameter \< 2.0 cm with conventional techniques or as \< 1.0 cm with spiral CT) * No known central nervous system metastases or carcinomatous meningitis PATIENT CHARACTERISTICS: Inclusion criteria * Life expectancy ≥ 12 weeks. * ECOG performance status 0-2 * ANC ≥ 1,500/mm³ * Platelet count ≥ 100,000/mm³ * SGOT ≤ 2.5 times upper limit of normal (ULN) (≤ 5 times ULN if liver metastases) * Total Bilirubin ≤ ULN for patients in group 3 and ≤ 2.0 times ULN for patients in groups 1 and 2 * Hemoglobin ≥ 9.0 g/dL * Creatinine ≤ 1.5 times ULN or creatinine clearance ≥ 60 mL/min * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception for the duration of study treatment * Willing to provide blood samples for mandatory translational studies Exclusion criteria * Known allergy to irinotecan hydrochloride-related agents (e.g., topotecan), 5-fluorouracil, and/or leucovorin calcium * Active or uncontrolled infection * Evidence of serious intercurrent illness (e.g., unstable angina, symptomatic congestive heart failure, serious uncontrolled cardiac arrhythmia) PRIOR CONCURRENT THERAPY: * Recovered from all toxicities * More than 4 weeks since prior major surgery * More than 2 weeks since completion of prior radiotherapy * No prior radiotherapy to \> 25% of bone marrow * More than 2 week since prior cytotoxic chemotherapy, biologic therapy, or immunotherapy * No concurrent sargramostim (GM-CSF)