PATIENT CHARACTERISTICS: Age: 17 and over Performance status: Karnofsky 60-100% Life expectancy: Not specified Hematopoietic: Not specified Hepatic: Bilirubin no greater than 1.5 mg/dL Renal: Creatinine no greater than 2.0 mg/dL OR Creatinine clearance at least 50 mL/min Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for at least 4 months after study No active serious infection that is not controlled by antibiotics No grade 3 or worse preexisting neurological abnormality, regardless of causality HIV negative