TLE1 expression in malignant mesothelioma

Malignant mesothelioma, an aggressive and often lethal tumor commonly associated with asbestos exposure, has been morphologically classified into epithelial, biphasic, and sarcomatoid subtypes. Histological distinction between biphasic or sarcomatoid mesothelioma and synovial sarcoma may be problematic in certain circumstances of intrathoracic location because of their similar clinicopathologic features, including not only their morphology but also occasional positive immunoreaction of mesothelioma markers. TLE1, which plays an important role in Wnt pathway, has been shown to be a specific marker for synovial sarcoma and diagnostically is useful; however, TLE1 expression in malignant mesotheliomas has not been fully evaluated. We immunohistochemically examined the expression of TLE1, factors related to the Wnt pathway including beta-catenin and cyclin D1, and mesothelioma markers including calretinin, HBME-1, cytokeratin 5/6, and thrombomodulin in 29 malignant mesotheliomas. TLE1 was variably expressed in 28 malignant mesotheliomas regardless of histomorphological subtype with > 25% of positive cells in 20 cases (69.0%). There was no evidence of association of TLE1 expression with immunoreactivity to other markers. Our study showed no or limited value of the immunohistochemical TLE1 expression in distinguishing malignant mesothelioma and synovial sarcoma.