Rituximab, Temozolomide, and Methylprednisolone in Treating Patients With Recurrent Primary CNS Non-Hodgkin's Lymphoma

DISEASE CHARACTERISTICS: Histologically confirmed primary CNS non-Hodgkin's lymphoma by brain biopsy, positive cerebrospinal fluid cytology, or vitrectomy Recurrent disease Measurable disease, define as bi-dimensionally measurable lesions with clearly defined margins by brain MRI or CT scan Radiographical evidence of tumor progression by MRI or CT scan Steroid therapy must be stable for 5 days prior to scan PATIENT CHARACTERISTICS: Age 18 and over Performance status Karnofsky 60-100% Life expectancy More than 8 weeks Hematopoietic WBC ≥ 3,000/mm^3 Absolute neutrophil count ≥ 1,500/mm^3 Platelet count ≥ 100,000/mm^3 Hemoglobin ≥ 10 g/dL (transfusion allowed) Hepatic SGOT < 2 times upper limit of normal (ULN) Bilirubin < 2 times ULN No active or latent hepatitis B infection Renal Creatinine < 1.5 mg/dL OR Creatinine clearance ≥ 60 mL/min Other Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No other malignancy within the past 3 years except nonmelanoma skin cancer or carcinoma in situ of the cervix No uncontrolled significant medical illness that would preclude study treatment No active infection No active HIV infection No concurrent disease that would dangerously alter drug metabolism or obscure toxicity PRIOR CONCURRENT THERAPY: Biologic therapy At least 7 days since prior interferon or thalidomide No concurrent prophylactic filgrastim (G-CSF) No concurrent immunotherapy Chemotherapy No prior temozolomide At least 14 days since prior methotrexate At least 21 days since prior procarbazine At least 42 days since prior nitrosoureas No other concurrent chemotherapy Endocrine therapy See Disease Characteristics At least 7 days since prior tamoxifen No concurrent hormonal therapy Radiotherapy No concurrent radiotherapy Surgery Not specified Other Recovered from all prior therapy At least 28 days since prior investigational agents At least 28 days since other prior cytotoxic therapy At least 7 days since other prior non-cytotoxic agents (e.g., tretinoin) (radiosenitizers allowed) No other concurrent investigational drugs