Immunoperoxidase staining of malignant cells in pleural effusions

The indirect immunoperoxidase method was used to detect the presence of carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA), keratin and alpha-1-antichymotrypsin (alpha 1ACT) in cells of pleural fluid sediments from 30 patients with pleural malignancies (18 mesotheliomas and 12 metastatic carcinomas). CEA was negative in all mesotheliomas and positive in all carcinomas but one (an ovarian serous cystadenocarcinoma); alpha 1ACT was positive in mesotheliomas and negative in carcinomas; EMA and keratin were positive in both types of tumor. These data suggest that the use of immunostaining against CEA and alpha 1ACT seems to improve the cytologic differential diagnosis between malignant mesothelioma and metastatic carcinoma in pleural effusions.