DISEASE CHARACTERISTICS: Histologically proven malignancy for which no curative therapy exists At least 1 bidimensionally measurable lesion No acute or chronic leukemia or multiple myeloma No active CNS metastases

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG-WHO 0-2 Life expectancy: At least 12 weeks Hematopoietic: Absolute neutrophil count greater than 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 9.0 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 elevations due to liver metastasis) Renal: Creatinine no greater than 1.5 times ULN Cardiovascular: No prior or concurrent QTc interval prolongation greater than 500 m/sec, unless approved by cardiology consult prior to study Other: No malabsorption syndrome due to surgery, prior disease, or other unknown reason No frequent vomiting or other medical condition that could interfere with oral medicine intake (e.g., partial bowel obstruction, external biliary diversion) No concurrent nonmalignant systemic disease making patient a poor risk for study No active uncontrolled infection Not pregnant or nursing Negative pregnancy test 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: No more than 2 prior chemotherapy regimens At least 4 weeks since prior chemotherapy (6 weeks since mitomycin or nitrosoureas) and recovered No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: At least 4 weeks since prior radiotherapy and recovered No prior wide field radiation (radiotherapy to at least 25% of bone marrow, including pelvic irradiation) No concurrent radiotherapy Surgery: Prior major gastrointestinal surgery allowed if recovered Other: At least 4 weeks since other prior investigational therapy and recovered