Value of immunocytochemistry in the study of malignant effusions.

Recognition of malignant effusion relies heavily on cytologic examination despite the difficulty of distinguishing atypical mesothelial hyperplasia from metastatic carcinoma. The combination of CEA, EMA, vimentin, keratin, high-molecular-weight cytokeratin (HMWK), low-molecular-weight cytokeratin (LMWK), and Alcian blue was tested in 51 cytologic specimens of pleural, peritoneal, and pericardial effusions. These showed metastatic carcinoma in 38 cases (ovary, 14; lung, 8; breast, 7; GI, 4; endometrium, 4; bladder, 1) and mesothelial processes in 13 (hyperplasia, 9; mesothelioma, 4). Strong positivity for EMA (92%), CEA (90%), and Alcian blue (71%) was noted in metastatic carcinoma but not in the mesothelial processes. Keratin was positive in all cases of mesothelioma but occurred also in mesothelial hyperplasias (44%) and metastatic carcinomas (47%). In mesothelial cells, HMWK was consistently stronger than LMWK, whereas in adenocarcinoma the reverse was true. There was no difference in the degree or distribution of positivity of any of the markers among the various primary sites of the neoplasms. Our findings are consistent with the view that immunocytochemistry with a battery of antibodies is useful in the recognition of malignant effusions but cannot, as yet, determine the site of origin of metastatic neoplasms.