SENSITIVITY OF HER-2 NEU ANTIBODIES IN ARCHIVAL TISSUE SAMPLES - POTENTIAL SOURCE OF ERROR IN IMMUNOHISTOCHEMICAL STUDIES OF ONCOGENE EXPRESSION/

HER-2/neu oncogene amplification and overexpression of breast cancer t issue has been correlated with poor prognosis in women with both node- positive and node-negative disease. However, several studies have not confirmed this association. Review of these studies reveals the presen ce of considerable methodological variability including differences in study size, follow-up time, techniques and reagents. The majority of papers with clinical follow-up information are immunohistochemical stu dies using archival, paraffin-embedded breast cancers, and a variety o f HER-2/neu antibodies have been used in these studies. Very little in formation, however, is available about the ability of the antibodies t o detect overexpression following tissue processing for paraffin-embed ding. Therefore, a series of antibodies, reported in the literature or commercially available, were evaluated to assess their sensitivity an d specificity as immunohistochemical reagents. Paraffin-embedded sampl es of 187 breast cancers, previously characterized as frozen specimens for HER-2/neu amplification by Southern blot and for overexpression b y Northern blot, Western blot, and immunohistochemistry, were used. Tw o multitumor paraffin-embedded tissue blocks were prepared from the pr eviously analyzed breast cancers as a panel of cases to test a series of previously studied and/or commercially available anti-HER-2/neu ant ibodies. Immunohistochemical staining results obtained with 7 polyclon al and 21 monoclonal antibodies in sections from paraffin-embedded blo cks of these breast cancers were compared. The ability of these antibo dies to detect overexpression was extremely variable, providing an imp ortant explanation for the variable overexpression rate reported in th e literature.