Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically proven CNS tumor that is refractory to conventional
therapy or for which no effective therapy is known

- Histological requirement may be waived for brainstem and optic gliomas

- Stratum 2: No bone marrow involvement

PATIENT CHARACTERISTICS:

- Age: 21 and under

- Performance status: Karnofsky 50-100% OR Lansky 50-100%

- Life expectancy: At least 8 weeks

- Absolute neutrophil count at least 1500/mm3

- Platelet count at least 100,000/mm3 (stratum 2: at least 125,000/mm3)

- Hemoglobin at least 8 g/dL

- Bilirubin less than 1.5 mg/dL

- SGOT/SGPT no greater than 2.5 times normal

- Creatinine or GFR normal for age

- If required, DLCO must be 80% of normal and patient old enough to cooperate for DLCO
test

- Neurologic deficits must be stable for at least 2 weeks prior to study

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception during and for 6 months after study

PRIOR CONCURRENT THERAPY:

- At least 7 days since prior biologic therapy or immunotherapy and recovered

- At least 6 months since prior bone marrow transplant (stratum 1 only)

- At least 7 days since prior growth factors

- No concurrent filgrastim (G-CSF) prophylaxis

- Stratum 2: No prior bone marrow transplantation

- At least 2 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosourea)
and recovered

- Stratum 2: No greater than 2 prior chemotherapy regimens

- No prior nitrosourea therapy

- If receiving dexamethasone, must be on stable or decreasing dose for at least 2 weeks
prior to study

- At least 2 weeks since prior local palliative radiotherapy (small port)

- At least 6 months since prior substantial bone marrow radiation, total body
irradiation, hemipelvic radiotherapy, or total abdominal/pelvic/chest or mantle/Y
ports radiotherapy

- Recovered from prior radiotherapy

- Stratum 2: No prior central axis radiation

- No other concurrent anticancer or investigational agents