BER-EP4 FOR DIFFERENTIATING ADENOCARCINOMA FROM REACTIVE AND NEOPLASTIC MESOTHELIAL CELLS IN SEROUS EFFUSIONS - COMPARISON WITH CARCINOEMBRYONIC ANTIGEN, B72.3 AND LEU-M1

OBJECTIVE: To evaluate the efficacy of Ber-EP4 in distinguishing epith elial cells from mesothelial cells in routine cytologic preparations. STUDY DESIGN: Paraffin-embedded cell blocks of serous effusions from 3 2 patients (11 metastatic adenocarcinomas, 16 reactive mesothelial pro liferations and 5 malignant mesotheliomas) were immunostained with Ber -EP4. For comparison, cell block preparations of adenocarcinomas and m esotheliomas were also immunostained with the most commonly applied ma rkers of adenocarcinoma: carcinoembryonic antigen (CEA), B72.3 and Leu -M1. In addition, cytocentrifuge preparations of 14 reactive effusions and 2 metastatic adenocarcinomas were stained prospectively with Ber- EP4. RESULTS: All adenocarcinomas showed intense membrane staining, wh ile all mesothelial proliferations, both benign and malignant, were ne gative. The Ber-EP4-positive immunostaining was remarkably clean, with very minimal nonspecific staining. CEA stained 11/11 adenocarcinomas, B72.3 stained 10/11, and Leu-M1 stained 8/11; mesotheliomas were nega tive with all three antibodies. CONCLUSION: Ber-EP4 is at least as use ful as CEA, B72.3 and Leu-M1 in the diagnosis of serous effusions. It has the advantage of high sensitivity and ease of interpretation becau se of the high percentage of tumor cells stained, characteristic membr anous staining and lack of cross-reaction with background inflammatory cells.