Chemotherapy in Treating Patients With Advanced Solid Tumors

DISEASE CHARACTERISTICS: Histologically or cytologically proven solid malignancy for which no curative therapy exists Glioblastoma eligible if following criteria are met: Stable performance status Stable symptoms At least 4 weeks on stable dose of dexamethasone CNS metastases allowed if no progression or no new edema present Measurable or evaluable disease No acute or chronic leukemia or multiple myeloma No known bone marrow involvement with tumor 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 PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior biologic therapy and recovered No prior allogeneic, syngeneic, or autologous bone marrow transplantation No prior peripheral blood stem cell transplantation No concurrent biologic therapy Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks for nitrosourea or mitomycin) and recovered No concurrent chemotherapy Endocrine therapy: See Disease Characteristics Radiotherapy: At least 4 weeks since prior radiotherapy to at least 25% of bone marrow (including pelvic irradiation) and recovered No concurrent radiotherapy Surgery: Prior major gastrointestinal surgery allowed (e.g., Whipple procedure) Other: At least 4 weeks since any prior investigational therapy At least 24 hours since prior alcohol consumption