Topotecan in Treating Young Patients With Neoplastic Meningitis Due to Leukemia, Lymphoma, or Solid Tumors

DISEASE CHARACTERISTICS: * Diagnosis of neoplastic meningitis secondary to leukemia, lymphoma (including AIDS-related lymphoma), or solid tumor (including primary CNS tumors or carcinomas of unknown primary site), defined by 1 of the following criteria: * Cerebral spinal fluid (CSF) cell count \> 5/μL AND evidence of blast cells on cytospin or by cytology (for patients with leukemia or lymphoma) * Presence of tumor cells on cytospin or cytology OR unequivocal presence of meningeal disease by MRI (for patients with solid tumor) * No conventional therapy for neoplastic meningitis exists * Patients with CNS leukemia or lymphoma must be refractory to conventional therapy, including radiotherapy (i.e., second or greater relapse) * Patients with CNS leukemia or lymphoma must have had a negative bone marrow aspiration within the past 2 weeks * No clinical evidence of obstructive hydrocephalus * No compartmentalization of CSF flow by radioisotope indium In 111 or technetium Tc 99 DTPA flow study * No ventriculoperitoneal or ventriculoatrial shunt unless patient is completely shunt-independent * No impending spinal cord compression or other CNS involvement (e.g., acute visual loss secondary to optic nerve involvement) requiring emergent local radiotherapy PATIENT CHARACTERISTICS: Age * 3 to 21 Performance status * Lansky 60-100% (≤ 16 years of age) OR * Karnofsky 60-100% (\> 16 years of age) Life expectancy * Not specified Hematopoietic * Not specified Hepatic * Not specified Renal * Calcium ≥ 7 mg/dL Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Sodium 125-150 mmol/L * Magnesium ≥ 0.7 mmol/L * Must have or be willing to have an intraventricular access device (i.e., Ommaya reservoir) * No uncontrolled infection * HIV-positive patients with AIDS-related lymphomatous meningitis are eligible * No other significant uncontrolled systemic medical illness that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy * Recovered from prior biologic therapy or immunotherapy Chemotherapy * Recovered from prior chemotherapy * At least 1 week since prior intra-colony stimulating factory (CSF) chemotherapy (2 weeks for liposomal cytarabine) * At least 3 weeks since prior systemic chemotherapy for leptomeningeal disease * Concurrent systemic chemotherapy to control systemic disease or bulk CNS disease allowed provided the systemic chemotherapy is not an investigational agent OR any of the following: * High-dose (\> 1 g/m\^2) methotrexate * High-dose (\> 1 g/m\^2) cytarabine * Fluorouracil * Capecitabine * Thiotepa * Nitrosoureas * Topotecan Endocrine therapy * Not specified Radiotherapy * See Disease Characteristics * At least 8 weeks since prior craniospinal radiotherapy and recovered * No concurrent CNS radiotherapy * Concurrent radiotherapy to extra-CNS sites (e.g., painful bone metastases not in the craniospinal axis) allowed Surgery * Not specified Other * More than 2 weeks since prior and no other concurrent investigational agents * No other concurrent intra-CSF or systemic therapy for leptomeningeal disease