DISEASE CHARACTERISTICS:

• Diagnosis of recurrent medulloblastoma or CNS germ cell tumor

  • Histologic review of the primary intracranial or spinal cord tumor required

    • Biopsy and reduction of tumor bulk prior to study encouraged but not required

• No more than 1 prior primary therapy (radiotherapy or chemoradiotherapy) and/or 1 prior salvage therapy

  • Patients with progression on salvage therapy ineligible
• Minimal residual disease (tumor bulk no more than 1.5 cm) or in second clinical complete remission (CR)
• Bone marrow infiltration with or without mass lesions or isolated abnormal CSF cytology as the only manifestation of recurrent disease allowed if a clinical CR is first achieved with conventional therapy

PATIENT CHARACTERISTICS:

Age:

• 2 to 25

Performance status:

• Karnofsky 80-100%

Life expectancy:

• More than 8 weeks

Hematopoietic:

• Absolute neutrophil count greater than 1,000/mm^3
• Platelet count greater than 100,000/mm^3

Hepatic:

• Bilirubin less than 1.5 mg/dL
• SGPT less than 80 IU

Renal:

• Creatinine less than 1.2 mg/dL

Cardiovascular:

• LVEF normal

Other:

• No infection
• Able to tolerate vigorous hydration
• Not pregnant
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• See Disease Characteristics
• Prior cyclophosphamide or ifosfamide allowed

Endocrine therapy:

• No concurrent dexamethasone as an antiemetic
• Other concurrent corticosteroids allowed

Radiotherapy:

• See Disease Characteristics
• Pretransplantation radiotherapy boost allowed

Surgery:

• See Disease Characteristics
• Pretransplantation surgery allowed

Other:

• At least 4 weeks since prior therapy except corticosteroids