Combination Chemotherapy Followed by Bone Marrow and/or Peripheral Stem Cell Transplantation in Treating Patients With Recurrent Medulloblastoma or CNS Germ Cell Tumors

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