Eligibility Criteria:
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