Epidermal growth factor receptor expression by acoustic neuromas.

Antibodies directed against epidermal growth factor receptor (EGFr) impede proliferation and induce differentiation of EGFr-positive cancers. To explore the effectiveness of anti-EGFr monoclonal antibodies on acoustic neuromas (ANs), we first sought to evaluate EGFr expression by ANs. The records of all patients with the diagnosis of AN at our institution from January 1989 to July 1994 were reviewed. Immunohistochemical analysis for EGFr was performed on formalin-fixed, paraffin-embedded 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 eighth cranial nerve was evaluated for background staining. Slides were scored as 0, +, ++, or and for percentage of positive cells by two pathologists, with Antoni A and Antoni B areas scored separately. Results demonstrate that most tumors are revealed to be EGFr positive with a mild degree of staining. Antoni A areas generally have greater staining than Antoni B regions, while normal eighth cranial nerves demonstrate minimal background staining. These results suggest that ANs express low levels of EGFr, with Antoni A areas having the highest levels. While further studies may more accurately quantitate EGFr levels in these tumors, the clinical efficacy of anti-EGFr-based therapies for ANs seems doubtful.