Correlation of Unilateral Sporadic Vestibular Schwannoma Growth Rates with Genetic and Immunohistochemical Abnormalities

Background: Unilateral sporadic vestibular schwannomas (USVS) are caused by inactivating somatic mutations of both alleles of the neurofibromatosis 2 (NF2) tumor suppressor gene. Unilateral sporadic vestibular schwannomas have a widely-varying growth patterns whose causes are poorly understood. Objective: We examined the relationships between an index of USVS growth, and genetic abnormalities and pathological growth indices. Subjects and Methods: Single-strand conformational polymorphism analysis and heteroduplex methods were used to screen for mutations in all 17 exons of the NF2 gene in USVS from 63 patients. Loss of heterozygosity (LOH) analyses were also carried out. An index of USVS growth (clinical growth index, CGI) was calculated as maximum tumor diameter divided by duration of symptoms. The immunohistochemical growth indices were based on monoclonal antibodies to Ki-67 and another tumor cell proliferation marker (platelet-derived growth factor (PDGF)). Results: CGI was highly variable and did not significantly decrease with increasing age at diagnosis. Either somatic NF2 mutations or LOH was found in 88% of tumors. PDGF and Ki-67 increased significantly with increasing age at diagnosis, and PDGF was lower in tumors with LOH than in those without LOH. In multiple linear regression analysis, CGI was significantly higher in people with higher PDGF, after accounting for age at diagnosis and LOH. Conclusion: An index of USVS growth increases with increasing PDGF, after accounting for age and LOH. Corresponding author.