DISEASE CHARACTERISTICS: Histologically confirmed recurrent or progressive brain tumors including the following: Anaplastic astrocytoma and glioblastoma multiforme Brain stem glioma Medulloblastoma or primitive neuroectodermal tumors present in supratentorial or posterior fossa locations Ependymoma Low grade gliomas Other Measurable or evaluable disease by CT or MRI OR Histologically confirmed previously untreated glial tumors including: Brain stem glioma Glioblastoma multiforme Measurable disease after surgery