Immunohistochemical staining for keratin and carcinoembryonic antigen in the diagnosis of malignant mesothelioma.

Using formalin-fixed, paraffin-embedded tissue and commercial antisera, we evaluated the usefulness of immunohistochemical staining for carcinoembryonic antigen (CEA) and keratin in the diagnosis of malignant mesothelioma. All 18 adenocarcinomas of lung examined stained for CEA, usually strongly, while only eight of 22 mesotheliomas stained for CEA and the staining was generally weak. Staining for keratin was observed in 10 of 22 mesotheliomas and 12 of 18 adenocarcinomas; there were no differences in intensity of staining between the groups. We conclude that strong diffuse staining for CEA favors a diagnosis of carcinoma, and negative staining for CEA is against a diagnosis of carcinoma, but these are relative and not absolute criteria. We find that staining for keratin is of no use in distinguishing these types of tumors.