Inclusion Criteria

DISEASE CHARACTERISTICS:

- Diagnosis of one of the following malignant brain tumors:

- Anaplastic astrocytoma

- Glioblastoma multiforme

- Anaplastic oligodendroglioma

- Medulloblastoma

- High-grade ependymoma

- Germ cell tumors

- Pineoblastoma

- Other primitive neuroectodermal tumors

- Recurrent disease or resistant to conventional therapy (e.g., surgery, radiotherapy,
or standard chemotherapy)

- No prior myeloablative doses of thiotepa OR

- Newly diagnosed malignant glioma with minimal residual disease after prior
radiotherapy

- Minimal residual disease is defined as tumor with maximum diameter of less than
1.5 cm by MRI and no corticosteroid dependency

PATIENT CHARACTERISTICS:

Age:

- Over 1 to under 50

Performance status:

- Karnofsky 70-100% OR

- Lansky 70-100%

Life expectancy:

- More than 12 weeks

Hematopoietic:

- Absolute neutrophil count at least 1,500/mm3

- Platelet count at least 100,000/mm3

- Hemoglobin at least 10 g/dL (transfusion allowed)

Hepatic:

- Bilirubin less than 1.5 times upper limit of normal (ULN)

- SGOT/SGPT less than 2.5 times ULN

- Alkaline phosphatase less than 2.5 times ULN

Renal:

- Creatinine less than 1.5 times ULN

- Creatinine clearance at least 70 mL/min

- BUN less than 1.5 times ULN

Cardiovascular:

- Ejection fraction greater than 50% OR

- Shortening fraction greater than 27%

- No evidence of myocardial ischemia on EKG if over 40 years of age

Other:

- HIV negative

- No AIDS-related illness

- No frequent vomiting or medical condition that would preclude oral medication (e.g.,
partial bowel obstruction)

- No other malignancy within the past 2 years except surgically cured carcinoma in situ
of the cervix or basal cell or squamous cell skin cancer

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- At least 2 weeks since prior biologic therapy or immunotherapy

Chemotherapy:

- See Disease Characteristics

- At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and
recovered

Endocrine therapy:

- See Disease Characteristics

Radiotherapy:

- See Disease Characteristics

- At least 6 weeks since prior radiotherapy and recovered

- At least 6 weeks since prior brachytherapy or radiosurgery

Surgery:

- See Disease Characteristics

- Recovered from prior major surgery