PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 70-100% Life expectancy: Greater than 12 weeks Hematopoietic: Absolute neutrophil count at least 2,000/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) AST or ALT no greater than 3 times ULN (no greater than 5 times ULN in patients with liver metastases) Renal: Creatinine clearance at least 50 mL/min Other: Able to swallow intact study capsules No active infection No life threatening illness (other than tumor) No prior malignancy within the past 5 years except well controlled nonmelanomatous skin cancer Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception