Etiologies

Both genetic predisposition and environmental agents are factors in the etiology of nervous system tumors. Inherited predisposition is supported by occurrences of specific brain tumors in families and by occurrences in inherited tumor syndromes. Structural changes in chromosomes and genetic alterations have been identified in a significant number of tumors. Two major classes of genes implicated in tumor pathogenesis are the oncogenes and the tumor suppressor genes. Chief oncogenes are the epidermal growth factor receptor (EGFR) gene on chromosome 7, the platelet-derived growth factor (PDGF) receptor gene, and a group of genes on chromosome 12q. An important tumor suppressor gene is the p53 on chromosome 17p. Potential tumor suppressor genes are located on chromosomes 1p, 9p, 10, 17p, 19q, and 22q. Tumor suppressor genes are involved in normal cell-cycle control, DNA repair, apoptosis, and the inhibition of angiogenesis. The activation of oncogenes by duplication or amplification, point mutation, and rearrangement, and the inactivation of tumor suppressor genes by mutations, physical loss, or deletion are common genetic alterations in nervous-system tumori-genesis. Genetic alterations may be inherited, or they may be acquired by the action of environmental agents.

Among environmental factors, irradiation to the head has been established as a potential risk for tumor development. An association between head trauma and brain tumor, particularly meningioma, has been suggested. Epstein-Barr virus has oncogenic potentials and is associated with primary central nervous system (CNS) lymphomas in HIV-infected patients. The papovavirus SV40 is implicated in the pathogenesis of choroids plexus papilloma and choroid plexus carcinomas. An association between brain tumors in human and various chemicals has been suggested but not proven.

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