Inclusion Criteria

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed advanced colorectal
adenocarcinoma Well differentiated OR Moderately well differentiated OR Poorly
differentiated Distant metastases not surgically curable Measurable disease No prior
treatment for disseminated disease No known brain metastases

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Zubrod 0-1 Life expectancy:
Not specified Hematopoietic: Absolute granulocyte count at least 1,500/mm3 Platelet count
at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times upper limit of normal
(ULN) SGOT or SGPT no greater than 2.5 times ULN Renal: Creatinine no greater than 2.0
mg/dL Other: Not pregnant or nursing Fertile patients must use effective contraception
Must be able to swallow or receive enteral medications through gastrostomy feeding tube No
intractable nausea or vomiting No other prior malignancy for the past 5 years except
adequately treated basal cell or squamous cell skin cancer, carcinoma in situ of the
cervix, or any adequately treated stage I or II cancer in complete remission

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior adjuvant
immunotherapy and recovered No concurrent immunotherapy Chemotherapy: At least 4 weeks
since prior adjuvant chemotherapy and recovered No other concurrent chemotherapy Endocrine
therapy: No concurrent hormonal therapy Radiotherapy: At least 4 weeks since prior
radiotherapy and recovered No more than 25% of total area of bone marrow irradiated No
concurrent radiotherapy Surgery: At least 2 weeks since prior surgery and recovered Other:
No concurrent proton pump inhibitors No other concurrent anticancer therapy