Caveolin-1 is a novel immunohistochemical marker to differentiate epithelioid mesothelioma from lung adenocarcinoma

Aims: The incidence of mesothelioma is increasing in Europe, Japan and other developing countries. There is difficulty in the accurate diagnosis of mesothelioma and its differentiation from lung adenocarcinoma. Mesothelioma shows a complex immunohistochemical profile. Therefore, the use of a immunohistochemical panel that includes both positive and negative mesothelial markers has become a general rule for its accurate diagnosis. However, they are still not sufficient. The aim was to assess the diagnostic utility of caveolin-1 (Cav-1), which is expressed in endothelial cells, alveolar type I pneumocytes and mesothelial cells, as a novel positive marker of mesothelioma. Methods and results: An immunohistochemical study of 80 cases of epithelioid mesothelioma and 80 cases of lung adenocarcinoma was performed for the analysis of the expression of Cav-1 and other markers. Cav-1 expression with a membranous and/or cytoplasmic pattern was found in all of the epithelioid mesothelioma. Of these, 42 cases (52.5%) showed Cav-1 expression in > 50% of tumour cells, 34 cases (42.5%) in 6-50% of tumour cells, and four cases (5.0%) in < 5% of tumour cells. In contrast, only six cases (7.5%) of lung adenocarcinoma showed focal Cav-1 expression in the cytoplasm of the tumour cells. The sensitivity and specificity of Cav-1 expression for the differentiation of epithelioid mesothelioma from lung adenocarcinoma were 100 and 92.5%, respectively. This is comparable or even superior to that of currently available positive markers such as calretinin or D2-40. Conclusions: Cav-1 is a novel immunohistochemical marker for the differentiation of epithelioid mesothelioma from lung adenocarcinoma.