Tissue expression of osteopontin (OPN) and mesothelin (MES) in malignant pleural mesothelioma (MPM). An immunohistochemical study of 70 consecutive cases

Abstract

e22102 Background: There is still no single test that can reliably identify malignant mesothelial cells. Recently soluble MES and OPN have been proposed as novel serum markers for MPM but a definitive consensus on their use in routine is still lacking. This study aims at 1. analysing the essential pathological features of a series of consecutive MPMs from a single institution and 2. assessing the tumour tissue expression of OPN and MES and speculating about the potential biological role of these molecules in MPM. Methods: All MPMs diagnosed between 1999 and 2008 were retrieved from the archives of the Pathology Unit of Alessandria Hospital. All the diagnoses had been made on the basis of conventional light microscopy features supplemented by a mucin stain (periodic acid-Schiff with and without diastase treatment) and a panel of immunostains (carcinoembryonic antigen, CD15/LeuM1, BerEP4, calretinin and cytokeratin 5). Immunostaining for OPN (polyclonal antibody) and MES (monoclonal antibody, clone 5B2) was performed using the labelled streptavidin-biotin method, and the staining intensity and extent were assessed. Results: The study group consisted of 50 males and 20 females with a mean age at diagnosis of 78.4 years (range 47–92). Histopathology was epithelial, mixed, and sarcomatous in 52, 12, and 6 patients respectively. OPN positivity (percentage of positive tumour cells >10%) was observed in 67 MPMs (96%) mostly in a granular cytoplasmic pattern and with an intensity ranging from weak (25%) to moderate (31%) and strong (44%). MES positivity (percentage of positive tumour cells >10%) was recorded in 60 MPMs (86%), of which 36% exhibited a weak, 36% a moderate and 28% a strong immunostaining in a membrane pattern. MES was positive in 100% of epithelial MPMs, in 67% of mixed and in 0% of sarcomatous. Positivity was restricted to the epithelial component in mixed MPMs. Conclusions: The high expression of OPN in MPM, irrespective of the histotype, seems to point to a role of this molecule as a marker of malignant transformation of mesothelial cells, while the restriction of positive staining for MES to the epithelial phenotype supports a role of MES as a marker of epithelial differentiation in MPM. No significant financial relationships to disclose.