Blood group antigens, Lewisx and Lewisy in the diagnostic discrimination of malignant mesothelioma versus adenocarcinoma.

Despite major advances in the differential diagnosis of mesotheliomas versus adenocarcinomas, a certain percentage defy diagnosis. Several markers such as keratin, carcinoembryonic antigen, Leu-M1, milk fat globulin, and antibody against tumor-associated glycoprotein Tag-72 (B72.3) have been used to distinguish them. In this study, blood group antigens, namely Lewisx and Lewisy, known to be expressed in a number of adenocarcinomas of diverse origin were used in the differential diagnosis of 30 samples from 18 mesotheliomas and 18 primary lung adenocarcinomas. Adenocarcinomas showed strong diffuse homogeneous staining, membranous staining, or both for Lewisy in 100% of cases irrespective of differentiation. Lewisx was expressed in 78% of adenocarcinomas with a wide variation in distribution of staining. Mesotheliomas did not show the diffuse homogeneous staining pattern but showed a markedly distinctive granular staining in the cytoplasm of rare cells in 23% of Lewisy and 20% of Lewisx cases, which was interpreted as negative. In conclusion, Lewisy is a sensitive marker for adenocarcinomas in that it stains 100% of cases and is a specific marker in the differential diagnosis of mesotheliomas and adenocarcinomas.