Evaluation of membranous staining of mesothelioma

Panels of immunohistochemical markers are often used to aid in categorizing malignant neoplasms involving the pleura. While epithelial membrane antigen (EMA) and human milk fat globule-2 (HMFG-2) are each reported to stain the majority of cases of adenocarcinoma and mesothelioma, authors have reported that the pattern of staining for these two antibodies can be a useful discriminant. Both are described as revealing a membranous pattern of staining for mesothelioma and a cytoplasmic staining pattern in adenocarcinoma. Immunostains were performed on 23 cases of malignant mesothelioma and 22 cases of adenocarcinoma. For EMA, 78% of mesotheliomas and 86% of adenocarcinomas stained positively, and 65% of mesotheliomas vs. 14% of adenocarcinomas exhibited a membranous staining pattern. For HMFG-2, 9% of mesotheliomas and 50% of adenocarcinomas stained positively, and 4% of mesotheliomas vs. 9% of adenocarcinomas exhibited a membranous staining pattern. Membranous staining for HMFG-2 was not a useful criterion. In this series, a membranous pattern of staining for EMA had a sensitivity of 65% and a specificity of 86% for the identification of malignant mesothelioma.