The use of immunoperoxidase panels for the cytologic diagnosis of malignancy in serous effusions.

The diagnostic value of an immunoperoxidase panel composed of antisera to carcinoembryonic antigen (CEA), epithelial membrane antigens (EMA), and high- and low-molecular-weight cytokeratins was evaluated on 39 consecutive pleural and peritoneal fluid specimens and correlated with routine cytologic and histochemical studies. The cases were classified into two groups: malignant (epithelial and small-cell undifferentiated carcinomas) and benign effusions. We found that the CEA and EMA antisera identified 91% and 100% of the epithelial malignancies, respectively. Mucin stains were positive in only 41% (mucicarmine) and 59% (Alcian blue) of these cases. The battery of cytokeratin markers identified malignant cells from 45%-100% of the cases but showed considerable positive staining of mesothelial cells. A selective review of the literature is presented along with recommendations for technical improvement in immunoperoxidase studies. We believe that an immunoperoxidase panel can be of considerable value in the cytologic diagnosis of epithelial malignancies in effusions. The panel composed of CEA and EMA can prove helpful in a routine cytology practice. Although the cytokeratin marker identified malignant cells, the concomitant immunostaining of mesothelial cells limits its utility. The commercially available panel can be a potential aid in improving the accuracy of serous fluid cytologic examination by decreasing both false-positive and false-negative diagnoses and thereby helping to prevent delays in diagnosis and treatment.