Inclusion Criteria

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