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