Temozolomide and Topotecan in Treating Patients With Primary CNS Lymphoma

Inclusion Criteria DISEASE CHARACTERISTICS: * Histologically confirmed primary CNS lymphoma at initial diagnosis * Measurable tumor by radiography * Failed\* OR is not a candidate for first-line high-dose systemic methotrexate-based chemotherapy with or without radiotherapy NOTE: \*Failure is defined as relapse, progression, or failure to achieve a complete response PATIENT CHARACTERISTICS: Age * 18 and over Performance status * Karnofsky 50-100% Life expectancy * Not specified Hematopoietic * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Hemoglobin ≥ 9 g/dL Hepatic * SGOT and SGPT ≤ 3 times upper limit of normal * Bilirubin ≤ 2.0 mg/dL Renal * Creatinine clearance \> 40 mL/min Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * HIV negative * No known allergy to temozolomide or topotecan * No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer or stage I or II cancer in complete remission * No other major medical illness or psychiatric impairment that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent prophylactic growth factors Chemotherapy * See Disease Characteristics * At least 6 weeks since prior nitrosoureas * At least 2 weeks since prior methotrexate Endocrine therapy * Not specified Radiotherapy * See Disease Characteristics Surgery * Not specified Other * Recovered from all prior therapy * At least 4 weeks since prior non-nitrosourea cytotoxic drugs (except methotrexate) * At least 4 weeks since prior systemic investigational agents * At least 2 weeks since prior non-cytotoxic antitumor drugs * No other concurrent antitumor therapy EXCLUSION CRITERA 1. Patients who are pregnant or breastfeeding, or females of childbearing potential not using adequate contraception. 2. Known allergy to temozolomide or topotecan. 3. Severe vomiting or other inability to administer medications orally. 4. Major medical illnesses or psychiatric impairment that in the investigator's opinion will prevent administration or completion of the protocol therapy and/or will interfere with follow-up.