Immunocytochemical Panel for the Identification of Malignant Cells in Serous Effusions

The cytologic diagnosis of malignancy in serous effusions can be challenging. An immunocytochemical (ICC) panel using commercially available antibodies (to carcinoembryonic antigen [CEA], epithelial membrane antigen [EMA], B72.3, Leu-M1, cytokeratin [CK], leukocyte common antigen [LCA], S-100 protein, and vimentin) was applied to cell blocks fixed in methyl Carnoy's solution that were from 55 consecutive pleural, peritoneal, and pericardial fluid specimens. The results were correlated with data from clinical records and routine cytologic studies. Final cytologic diagnoses included 26 of adenocarcinoma and 1 of mesothelioma. The remaining 28 cases were considered to be benign (reactive) proliferations. EMA, CEA, B72.3, and Leu-M1 were present in 96%, 77%, 58%, and 42% of adenocarcinomas, respectively. These determinants were absent in the mesothelioma and the reactive effusions, although anti-CEA yielded strong background staining of inflammatory cells. The CK markers identified malignant cells in 93% of cases, but consistently stained mesothelial cells as well. Antivimentin strongly labeled mesothelial cells in all cases, with weak to absent staining of malignant cells. In 3 of 26 carcinoma cases (12%), the ICC panel identified malignant cells that were not recognized initially on routine cytologic examination. In 1 of 26 cases (4%), the panel was falsely negative. Use of this approach can improve the diagnostic accuracy of cytologic examination of serous fluids. The ICC panel is especially helpful when atypical mesothelial proliferation is present, or in cases that are clinically suspect for malignancy, but cytologically negative because there are only a few malignant cells, or those that are cytologically bland.