PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: Not specified Hematopoietic: Absolute neutrophil count greater than 1500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 9 g/dL Hepatic: Bilirubin no greater than 2.0 mg/dL SGOT or SGPT no greater than 3 times upper limit of normal (ULN) (5 times ULN if due to liver metastases) Renal: Creatinine no greater than 1.5 mg/dL Other: No malabsorption syndrome due to prior surgery, gastrointestinal disease, or other unknown reason No concurrent nonmalignant systemic disease No active uncontrolled infection No frequent vomiting or medical condition that could interfere with oral medication uptake (e.g., partial bowel obstruction, bowel resection, partial intestinal bypass, external biliary diversion) No prior or concurrent malignancies at other sites except carcinoma in situ of the cervix or adequately treated basal or squamous cell skin cancer HIV negative No AIDS-related illness Not pregnant or nursing Fertile patients must use effective contraception