Immunohistochemical panel for distinguishing between carcinoma and reactive mesothelial cells in serious effusions.

This study was designed to assess whether a new panel of antibodies is a useful adjunct in the differential diagnosis of carcinoma and reactive mesothelial cells. Complete, one-hour immunohistochemistry using antibodies against cytokeratin (CK), carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA) and fibronectin was applied to cell blocks from 76 pleural and peritoneal fluid specimens. Fifty patients with histologically diagnosed primary carcinomas and 26 without evidence of malignancy were included. The results were correlated with routine cytologic results. The final cytologic diagnoses were 28 malignant effusions and 48 benign effusions. CEA and EMA were present in 25 (89%) and 24 (86%) of 28 carcinoma cases, respectively. These determinants were absent from reactive mesothelial cells. Fibronectin strongly labeled reactive mesothelial cells, with no staining of carcinoma cells. Carcinoma cells expressed at least two antibodies to CK, CEA and EMA and were negative to fibronectin. Reactive mesothelial cells expressed both CK and fibronectin. In 6 of 28 carcinoma cases (21%) the immunohistochemical panel identified carcinoma cells that were not recognized initially on routine cytologic examination. A panel of CEA, EMA and fibronectin monoclonal antibodies appears to be suitable for distinguishing between carcinoma cells and reactive mesothelial cells in serous effusions.