DIFFERENTIAL EXPRESSION OF N-CADHERIN IN PLEURAL MESOTHELIOMAS AND E-CADHERIN IN LUNG ADENOCARCINOMAS IN FORMALIN-FIXED, PARAFFIN-EMBEDDED TISSUES

The differential diagnosis of pleural mesotheliomas and lung adenocarc inomas presents a continued challenge in the practice of surgical path ology. Paraffin immunohistochemistry (MC) using different panels of an tibodies can be helpful in some cases, but, as yet, no antigen is expr essed specifically in mesotheliomas nor in adenocarcinomas. Using well characterized monoclonal antibodies (MAb) that recognized distinct me senchymal and epithelial adhesion proteins, N-cadherin (13A9 MAb) and E-cadherin (E9 MAb), respectively, we found previously that in frozen- section IHC mesotheliomas and adenocarcinomas had distinct cadherin ph enotypes: mesotheliomas were positive for N-cadherin, and lung adenoca rcinomas were positive for E-cadherin. Using antigen-retrieval methods , we successfully extended our study to formalin-fixed, paraffin-embed ded tissue sections. Tumors from 28 patients (14 originally diagnosed as mesotheliomas, and 14 diagnosed as adenocarcinomas) were stained wi th 13A9 MAb and E9 MAb. Review of hematoxylin-eosin sections excluded from analysis one case previously diagnosed as mesothelioma, which rep resented a hemangiopericytoma Of the remaining 27 cases, 12 of 13 meso theliomas were positive for N-cadherin and negative for E-cadherin. Th e exception was a multifocal microscopic papillary tumor of apparent m esothelial origin, which was negative for both N-cadherin and E-cadher in. Conversely, 13 of 14 adenocarcinomas were E-cadherin positive and N-cadherin negative except for one adenocarcinoma with focal N-cadheri n expression. One case of a poorly differentiated adenocarcinoma invad ing skeletal muscle was negative for both 13A9 and E9. These studies c onfirmed the utility of the cadherin antibodies in distinguishing pleu ral mesotheliomas from lung adenocarcinomas. The reactivity of the cad herin-specific antibodies with antigens in paraffin sections make them powerful and reliable markers in the practice of diagnostic surgical pathology. Copyright (C) 1997 by W.B. Saunders Company.