Immunohistochemical determination of HER-2/neu expression in invasive breast carcinoma

Numerous methods exist for HER-2/neu assessment; however; technical and int erpretive standardization is virtually absent. We evaluated 2 commercially available antibodies on routinely fixed paraffin-embedded tissue sections t o establish our own guidelines. Thirty-three cases of infiltrating breast c arcinoma were evaluated simultaneously with monoclonal and polyclonal antib odies. Only membranous staining, no matter how focal, was considered positi ve. An additional 32 tumors were studied subsequently using only the polycl onal antibody. Of all carcinomas, 13.0% showed immunohistochemical evidence of HER-2/neu overexpression. High-grade tumors were more often positive. T here was no HER-2/neu gene expression in the benign epithelium that general ly was present in the tissue section or in any of the well-differentiated t urners tested. The polyclonal antibody proved more sensitive than the monoc lonal antibody. While true cytoplasmic staining was present occasionally, i t did not create substantial difficulty in interpretation. The polyclonal a ntibody cost substantially less than the monoclonal antibody. Fluorescence in situ hybridization assay for HER-2/neu gene amplification performed on 3 2 of 65 cases showed concordant results in 31 cases. The immunohistochemica l assay for HER-2/neu gene overexpression, using our methods, is accurate, economic, and easily integrated into the laboratory.