PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 70-100% Life expectancy: More than 8 weeks Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 10 g/dL (may be transfusion dependent) Hepatic: Bilirubin less than 2 times upper limit of normal (ULN) SGOT less than 2 times ULN Renal: Creatinine less than 1.5 mg/dL Creatinine clearance at least 60 mL/min Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective barrier contraception during and for at least 2 months after study Able to swallow capsules No active infection No disease or other serious concurrent medical illness that would preclude study