Pemetrexed Disodium in Treating Patients With Recurrent Malignant Gliomas, Primary CNS Lymphoma, or Brain Metastases

DISEASE CHARACTERISTICS: * Diagnosis of 1 of the following: * Malignant glioma, including the following subtypes: glioblastoma or gliosarcoma, anaplastic astrocytoma, anaplastic oligodendroglioma, anaplastic mixed glioma, or malignant glioma not otherwise specified, meeting the following criteria: * Not required to have measurable or evaluable disease * Must have failed prior radiation therapy \> 4 weeks ago * Must have failed at least 1 prior chemotherapy regimen * Confirmation of tumor progression by MR spectroscopy, PET scan, or biopsy/resection if prior radiosurgery was performed * Primary CNS lymphoma, meeting the following criteria: * Measurable disease as defined by bidimensionally measurable lesions with clearly defined margins by CT scan or MRI * Must have failed at least one prior chemotherapy regimen * Must have failed at least one agent or regimen * Brain metastases from a solid tumor, meeting the following criteria: * Measurable disease as defined by bidimensionally measurable lesions with clearly defined margins by CT scan or MRI * Biopsy is not required if radiographic imaging is consistent with brain metastases * Must have failed prior whole-brain radiotherapy * Patients with leptomeningeal metastases with or without brain metastases are eligible for therapy (may be diagnosed by MRI or cytology) * Confirmation of tumor progression by MR spectroscopy, PET scan, or biopsy/resection if prior radiosurgery was performed * Effusions or fluid collections must be drained prior to study entry PATIENT CHARACTERISTICS: * Karnofsky performance score ≥ 60 * WBC \> 3,000/mm\^3 * Absolute neutrophil count \> 1,500/mm\^3 * Platelet count \> 100,000/mm\^3 * Hemoglobin \> 10 mg/dL (transfusion allowed) * SGOT/SGPT \< 3.0 times upper limit of normal (ULN) * Bilirubin \< 1.5 times ULN * Creatinine \< 1.5 mg/dL * Creatinine clearance \> 45 mL/min * Women of childbearing potential and sexually active males must commit to the use of effective contraception while on study and for 3 months after completing study treatment * Women who are pregnant or breast-feeding are not eligible for study treatment * Negative pregnancy test * Able to take steroids, vitamin B12, or folate * No significant medical illnesses or infection that, in the investigator's opinion, cannot be adequately controlled with appropriate therapy or would compromise the patient's ability to tolerate this therapy * Only one active tumor type allowed, except nonmelanoma skin cancer or carcinoma in situ of the cervix * A history of other malignancies are acceptable if in complete remission and off all therapy for that disease for a minimum of 3 years PRIOR CONCURRENT THERAPY: * See Disease Characteristics * More than 4 weeks since prior whole-brain or other radiotherapy * Recovered from any side effects (6 weeks for a nitrosourea; 4 weeks for temozolomide, procarbazine, etoposide or experimental agent; 3 weeks for isotretinoin or tamoxifen) (for patients with gliomas) * No more than 2 prior chemotherapeutic agents or regimens (includes biologic agents) (for patients with gliomas) * Recovered from prior biopsy or re-resection of the tumor (10-14 days for resection or 3-5 days for a biopsy) (for patients with gliomas) * May not be on any other chemotherapy except for hormonal therapy or trastuzumab (Herceptin®) (for patients with brain metastases) * No limitations on prior CNS-directed therapies (for patients with brain metastases) * Able to discontinue nonsteroidal anti-inflammatory drugs (NSAIDs) * Patients taking NSAIDs or aspirin are required to interrupt therapy for at least 2 days before the study treatment and 2 days after the infusion