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