Chemical- and virus-induced brain tumors.

Experimental animal models resembling most human brain tumor types can be induced by exposure to oncogenic viruses or chemical carcinogens: Astrocytomas and glioblastoma multiforme can be produced experimentally by intracerebral injection of oncornaviruses, whereas medulloblastomas, choroid plexus papillomas, and ependymomas can be induced by the papovaviruses. Adenoviruses have been utilized to cause medulloepitheliomas, neuroblastomas, and retinoblastomas. All three groups of viruses can result in sarcoma production. Gliomas represent the primary tumor type induced in the brain by chemical carcinogens. These autochthonous tumor systems are reviewed, with emphasis on methods, tumor type, latency period, advantages, and disadvantages. In addition, recent investigations of molecular events involved in neoplastic transformation by chemical carcinogens are summarized.