Monoclonal antibody Ber‐EP4: Its use in the differential diagnosis of malignant mesothelioma and carcinoma in cell blocks of malignant effusions and FNA specimens

Formal sublimate‐fixed cell blocks derived from 129 malignant pleural (and some peritoneal) effusions, 8 benign effusions with reactive mesothelial cells, and 23 FNA specimens, were immunostained with monoclonal antibody Ber‐EP4 to assess its ability to distinguish malignant mesothelioma (MM) from carcinoma. Only 2 of 44 (4%) well‐characterized MM were Ber‐EP4 + , while none of 8 benign mesothelial proliferations reacted with the antibody. Fifty‐seven percent of 23 pulmonary adenocarcinomas (AC) and 60% of 43 pulmonary carcinomas of all other histological types were Ber‐EP4 + . Of 40 metastatic AC originating from breast, gastrointestinal tract, ovary, endometrium, and kidney, 80% were Ber‐EP4 + . The predictive value of positive Ber‐EP4 staining in distinguishing AC from MM was 96%. The predictive value of a negative Ber‐EP4 in excluding MM was 70%, when the differential diagnosis was adenocarcinoma. These results suggest that Ber‐EP4 is helpful in differentiating MM and AC if used together with other discriminating antibodies. © 1994 Wiley‐Liss, Inc.