The value of immunohistochemistry of pleural biopsy specimens in the differential diagnosis between malignant mesothelioma and metastatic carcinoma.

The aim of the present study was to evaluate the aid of immunohistochemistry in the differential diagnosis between pleural malignant mesothelioma (MM) and secondary pleural carcinoma in pleural biopsy specimens. A series of MM (epithelial or biphasic type) (n = 39), and a series of secondary pleural carcinomas (n = 25) were studied with a panel of monoclonal antibodies against Ber-EP4, CEA, and Leu-MI (CD-15). Considering the markers one, two or three at a time, computer analysis was conducted to identify the immunophenotype with the highest sensitivity and specificity for both MM (n = 39) and adenocarcinoma (n = 19). The CEA/CD-15 marker combination had the highest specificity (MM = 100%; adenocarcinoma = 82.1%), and sensitivity (MM = 82.1%; adenocarcinoma = 100%) considering both categories of tumours. Positive reaction for CEA and/or CD-15 was the best indicator of metastatic adenocarcinoma. Negative reaction for CEA/CD-15 and Ber-EP4/CD-15 showed up to be 100% specific for MM. Positive reaction for one, two or even all these antigens, however, occurred in nine tumours predetermined as MM according to their gross appearance, and absence of other primary malignancies at autopsy. Ultrastructural examination (n = 7) of these tumours strongly supported the diagnosis in one case, and did by no means exclude the diagnosis MM in the other six cases. Neither did any of the tumours reveal ultrastructural signs of adenomatous differentiation, and they did not express PAS/diastase resistant globules, amylase or surfactant. Anti -Ber-EP4 was the antibody most frequently expressed in MM (n = 8). Until antibodies specific for MM are available, the limitation of immunohistochemistry to solve the diagnosis in all cases of pleural malignant tumours has to be considered.