DISEASE CHARACTERISTICS: Primary central nervous system non-Hodgkin's lymphoma (PCNSL) Clinically diagnosed intracranial space-occupying lesion Pathology consistent with non-Hodgkin's lymphoma and reviewed by NCCTG Biopsy optional if characteristic history, pathognomonic neuroimaging, and cytology are consistent with malignant lymphocytes from vitrectomy, CSF, or both No occult systemic lymphoma or prior lymphoma No post-transplant lymphoproliferative disorder Disease measurable or evaluable on postoperative contrast-enhanced CT or MRI Postoperative therapy must start within 6 weeks of definitive diagnosis