Combination Chemotherapy in Treating Patients With Colorectal Cancer

DISEASE CHARACTERISTICS: Histologically confirmed adenocarcinoma of the colon or rectum Metastatic, locally advanced, or recurrent disease Patients must have at least 2 generations (parents and grandparents) who belong to one of the following racial groups: Asian or Pacific Islander (e.g., China, Japan, Korea, the Philippine Islands, or Samoa) Black (originating from the black racial groups of Africa) Hispanic (originating from Mexico, Puerto Rico, Cuba, Central or South America, or other Spanish culture) White (originating from the peoples of Europe, North Africa, or the Middle East) No patients with parents or grandparents of mixed race or race other than that of the patient PATIENT CHARACTERISTICS: Age: Not specified Performance status: CTC 0-2 Life expectancy: Not specified Hematopoietic: Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 mg/dL AST no greater than 3 times upper limit of normal Renal: Creatinine no greater than 1.5 mg/dL Other: Not pregnant or nursing Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Prior adjuvant fluorouracil allowed if relapse occurred at least 6 months after completion of fluorouracil At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) No prior irinotecan No other concurrent chemotherapy Endocrine therapy: No concurrent hormones except steroids for adrenal failure, hormones for nondisease related conditions (e.g., insulin for diabetes), or intermittent dexamethasone as an antiemetic No concurrent prednisone Radiotherapy: At least 4 weeks since prior radiotherapy (except to bone or soft tissue involving less than 25% of bone marrow) No concurrent radiotherapy Surgery: At least 4 weeks since prior major surgery Other: No concurrent phenobarbital, valproate, or cyclosporine None of the following concurrently during first course of therapy: Macrolide antibiotics (e.g., azithromycin, erythromycin, clarithromycin, troleandomycin, dapsone) Azole antibiotics (e.g., fuconazole, miconazole, itraconazole, ketoconazole) Triazobenzodiazepines (e.g., alprazolam, midazolam, triazolam) Antidepressants (e.g., fluoxetine, setraline hydrochloride, fluoxamine, nefazodone hydrochloride) Quinolone antimicrobials (e.g., ciprofloxacin, ofloxacin) Imidazole antibiotics (e.g., clotrimazole) Anti-ulcer medications (e.g., omeprazole, lansoprazole) Ethinyl estradiol Diltiazem Cimetidine hydrochloride Cisapride Terfenadine Rifampin Glucocorticoids Antiepileptics Grapefruit juice