EPIDERMAL GROWTH-FACTOR RECEPTOR EXPRESSION BY ACOUSTIC NEUROMAS

Antibodies directed against epidermal growth factor receptor (EGFr) im pede proliferation and induce differentiation of EGFr-positive cancers , To explore the effectiveness of anti-EGFr monoclonal antibodies on a coustic neuromas (ANs), we first sought to evaluate EGFr expression by ANs. The records of all patients with the diagnosis of AN at our inst itution from January 1989 to July 1994 were reviewed. Immunohistochemi cal analysis for EGFr was performed on formalin-fixed, paraffin-embedd ed archival surgical specimens. Skin, liver, and placenta were used as positive tissue controls. Purified rabbit immunoglobulin G replacing the experimental antibody acted as a negative control, and normal eigh th cranial nerve was evaluated for background staining. Slides were sc ored as 0, +, ++, or +++ and for percentage of positive cells by two p athologists, with Antoni A and Antoni B areas scored separately. Resul ts demonstrate that most tumors are revealed to be EGFr positive with a mild degree of staining. Antoni A areas generally have greater stain ing than Antoni B regions, while normal eighth cranial nerves demonstr ate minimal background staining, These results suggest that ANs expres s low levels of EGFr, with Antoni A areas having the highest levels, W hile further studies may more accurately quantitate EGFr levels in the se tumors, the clinical efficacy of anti-EGFr-based therapies for ANs seems doubtful.