PATIENT CHARACTERISTICS: Age: 12 and over Performance status: WHO 0-1 Life expectancy: At least 3 months Hematopoietic: Neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than upper limit of normal (ULN) Alkaline phosphatase no greater than ULN OR Alkaline phosphatase liver fraction and 5'-nucleotidase no greater than ULN AST/ALT less than 2.5 times ULN Albumin greater than 25 g/L No clinically significant liver disease Renal: Creatinine no greater than 1.5 mg/dL OR Creatinine clearance at least 40 mL/min Cardiovascular: No congestive heart failure or angina pectoris even if medically controlled No myocardial infarction within past year No uncontrolled arterial hypertension No arrhythmias Other: Not pregnant or nursing Fertile patients must use effective contraception No history of other malignancy except basal cell carcinoma or carcinoma in situ of the cervix No other serious illness or medical conditions (e.g., history of significant neurological or psychiatric disorders, active infection) No concurrent grapefruit consumption on a regular basis