Neurotrophic factor expression in vestibular schwannoma. An overview

The vestibular schwannoma is a benign, slow-growing neoplasm that originates from the neurolemmal sheath of the vestibular branch of the VIIIth cranial nerve. This tumor entity accounts for 6 % of all intracranial tumors and the annual incidence of newly diagnosed vestibular schwannoma is reported as 13 per million. The molecular pathogenesis of both sporadic vestibular schwannoma and those occurring in neurofibromatosis type II appears to be associated with an aberration of a tumor suppressor gene on chromosome 22q12. The biological background for the various growth patterns of vestibular schwannoma is, however, largely unknown. This differing clinical and biological behaviour of vestibular schwannoma may be explained by the presence of neurotrophic factors. The results of recent immunohistochemical studies demonstrate the co-expression of transforming growth factor (TGF)-beta 1 and glial cell line-derived neurotrophic factor (GDNF) in vestibular schwannoma and suggest a trophic synergism of both neurotrophic factors in this tumor. Moreover, expression of numerous different neurotrophic factors has been shown in studies of nerve growth factor (NGF), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), fibroblast growth factor (FGF), neuregulin (NRG) and erythropoietin (EPO) indicating a biological role in development, maintainance or growth of vestibular schwannoma. In this article, we summarize the findings on neurotrophic factor expression and discuss their characteristics and biological role in vestibular schwannoma.