THE IMMUNOHISTOCHEMICAL DIAGNOSTIC PANEL FOR EPITHELIAL MESOTHELIOMA - A REEVALUATION AFTER HEAT-INDUCED EPITOPE RETRIEVAL

The immunohistochemical diagnosis between epithelial mesothelioma and adenocarcinoma is currently based on the use of a panel of antibodies to adenocarcinoma-associated antigens and a few antibodies to mesothel ial-associated antigens. Since the introduction of epitope retrieval m ethods, the sensitivity of many antibodies has been enhanced. Thus, a reevaluation of the mesothelioma/adenocarcinoma diagnostic panel becom es necessary. We studied 268 paraffin-embedded formalin-fixed tumor sa mples that included 57 epithelial mesotheliomas and 211 adenocarcinoma s of various origins, comparing an extensive antibody panel with and w ithout heat-induced epitope retrieval (HIER). Marked increase in the s ensitivity of several antibodies, with no loss of specificity, was fou nd when HIER was used. After statistical analysis, the antibodies to t he epithelial glycoproteins carcinoembryonic antigen, BerEp4, and Bg8 emerged as the best discriminators between adenocarcinoma and epitheli al mesothelioma within the entire panel. The mesothelium-associated an tibodies, HBME-1, calretinin, and thrombomodulin were less sensitive a nd less specific than the former, although they were found to be usefu l on certain cases. Antibodies to cytokeratins and vimentin, although of minor diagnostic value in this context, may be helpful to evaluate the quality of antigen preservation. This study confirms the value of immunohistochemistry to accurately distinguish mesothelioma from adeno carcinoma when an antibody panel approach is used. The addition of hea t-induced epitope retrieval methods increases the effectiveness of the procedure and is recommended for most of the antibody panel members.