PATIENT CHARACTERISTICS: Age: Over 18 Performance status: 0-2 Life expectancy: Greater than 4 months Hematopoietic: See Disease Characteristics Hepatic: Bilirubin less than 1.5 times normal (unless due to hemolysis or ineffective erythropoiesis) AST and ALT less than 2 times normal Renal: Creatinine less than 1.5 times normal Cardiovascular: No uncontrolled or severe congestive heart failure Pulmonary: Serum CO2 greater than 18 mmHg Other: No uncorrected folate or vitamin B12 deficiency HIV negative No other medical or psychiatric illness that would preclude study At least 3 years since prior nonleukemic malignancy Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception