Rituximab in Treating Patients With Refractory or Relapsed Primary CNS Lymphoma

DISEASE CHARACTERISTICS: Histologically confirmed primary CNS lymphoma based on 1 of the following: Histologically confirmed non-Hodgkin's B-cell lymphoma by brain biopsy or resection Positive cerebrospinal fluid (CSF) cytology or immunohistochemical diagnosis of CSF monoclonality with or without measurable intracranial disease Histologically confirmed vitreal lymphoma with measurable intracranial tumor CD20 positive by brain biopsy Measurable (greater than 1 cm in diameter) tumor by CT scan or MRI Progressed during first-line chemotherapy and/or radiotherapy OR relapsed after initial successful treatment No systemic lymphoma by CT scan of the chest, abdomen, and pelvis with contrast No leptomeningeal lymphoma by lumbar puncture for CNS cytology/flow cytometry No ocular lymphoma by slit lamp examination PATIENT CHARACTERISTICS: Age 18 and over Performance status Karnofsky 60-100% Life expectancy Not specified Hematopoietic Absolute neutrophil count at least 1,500/mm^3 Platelet count at least 100,000/mm^3 Hemoglobin at least 9.0 g/dL Hepatic Bilirubin less than 1.5 mg/dL Transaminases less than 4 times upper limit of normal Renal Creatinine less than 1.5 mg/dL Other Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 1 year after study participation HIV negative Mini mental status examination score at least 15 No concurrent serious infection No other medical illness that would preclude study treatment No other malignancy within the past 5 years except curatively treated basal cell or squamous cell skin cancer or carcinoma in situ PRIOR CONCURRENT THERAPY: Biologic therapy More than 90 days since prior biologic therapy No prior rituximab No concurrent prophylactic growth factors (e.g., filgrastim [G-CSF] or sargramostim [GM-CSF]) Chemotherapy See Disease Characteristics At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas) Endocrine therapy Not specified Radiotherapy See Disease Characteristics At least 3 months since prior radiotherapy Surgery Not specified Other Recovered from prior therapy More than 90 days since prior investigational drugs More than 90 days since prior use of a therapeutic device