Background: Malignant pleural mesothelioma (MPM) is a highly aggressive tumour with poor prognosis and Limited response to therapy. MPM is characterised by complex chromosomal aberrations, including chromosome 10 losses. The tumour suppressor gene phosphatase and tensin homologue deleted from chromosome 10 (PTEN) located on chromosome 10q23 plays an important role in different cancer, but its relevance for MPM is unclear. Patients and methods: In the present tissue microarray-based study, 341 MPM were studied for PTEN expression by immunohistochemistry using a monoclonal mouse PTEN antibody. Expression levels were semiquantitatively scored (negative, weak, moderate, strong). Expression of PTEN was correlated to overall survival. Results: Clinical data from 206 patients were available. One hundred and five patients were stage T4 and 92 patients presented with regional and mediastinal lymph node metastasis. Loss of PTEN expression was observed in 62% of the cases. The survival time was correlated to PTEN expression in 126 cases with complete follow-up data. Comparing any PTEN expression versus no expression, median survival time was significantly Longer (log rank test p = 0.0001) in patients with PTEN expression (15.5 months; 95% Cl: 3.8; 27.2 vs 9.7 months; 95% Cl: 7.9; 11.7). Cox regression analysis revealed an association between PTEN expression and survival to = 0.003) independently from the histological subtype (p = 0.7). Conclusion: PTEN is an independent prognostic biomarker in mesothelioma patients. The frequent toss of expression of the tumour suppressor gene PTEN suggests involvement of the PI3K-AKT/protein kinase B (PKB) pathway in MPMs, which may be relevant for future mesothelioma treatment. (c) 2008 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.

Anti-calretinin antibodies are useful to differentiate adenocarcinomas from malignant mesotheliomas of the lung. Therefore, calretinin expression is rarely reported for sarcomatoid mesotheliomas. Anti-podoplanin antibodies (eg D2-40) react with lymphatic endothelia, Kaposi's sarcoma, lymphangioma and mesotheliomas. For the interpretation of spindle cell lesions of the pleura, knowledge of calretinin and D2-40 expression frequencies in sarcomatoid mesothelioma is desirable. To systematically investigate the sensitivity of calretinin and D2-40 antibodies in epithelioid and sarcomatoid areas of malignant mesotheliomas, a tissue microarray with 341 malignant mesotheliomas, including 112 epithelioid, 46 sarcomatoid and 183 biphasic tumors was constructed. Epithelioid and sarcomatoid differentiated tumor areas were clearly separated within the tissue microarray. Expression of calretinin and D2-40 was separately studied in epithelioid and sarcomatoid areas by immunohistochemistry. Calretinin expression was found in 91% of epithelioid and 57% of sarcomatoid tumor areas. D2-40 immunostaining was present in 66% of the epithelioid and 30% of the sarcomatoid tumor areas. A combination of calretinin and D2-40 increased the sensitivity in epithelioid tumor areas to 0.96 and in sarcomatoid tumor areas to 0.66. These data indicate that a combination of calretinin and D2-40 will improve diagnostic accuracy for spindle cell lesions of the pleura, whereas almost all epithelioid mesotheliomas are identified by calretinin alone.

The association of simian virus 40 (SV40) with malignant pleural mesothelioma is currently under debate. In some malignancies of viral aetiology, viral DNA can be detected in the patients' serum or plasma. To characterize the prevalence of SV40 in Swiss mesothelioma patients, we optimized a real-time PCR for quantitative detection of SV40 DNA in plasma, and used a monoclonal antibody for immunohistochemical detection of SV40 in mesothelioma tissue microarrays. Real-time PCR was linear over five orders of magnitude, and sensitive to a single gene copy. Repeat PCR determinations showed excellent reproducibility. However, SV40 status varied for independent DNA isolates of single samples. We noted that SV40 detection rates by PCR were drastically reduced by the implementation of strict room compartmentalization and decontamination procedures. Therefore, we systematically addressed common sources of contamination and found no cross-reactivity with DNA of other polyomaviruses. Contamination during PCR was rare and plasmid contamination was infrequent. SV40 DNA was reproducibly detected in only 4 of 78 (5.1%) plasma samples. SV40 DNA levels were low and not consistently observed in paired plasma and tumour samples from the same patient. Immunohistochemical analysis revealed a weak but reproducible SV40 staining in 16 of 341 (4.7%) mesotheliomas. Our data support the occurrence of non-reproducible SV40 PCR amplifications and underscore the importance of proper sample handling and analysis. SV40 DNA and protein were found at low prevalence (5%) in plasma and tumour tissue, respectively. This suggests that SV40 does not appear to play a major role in the development of mesothelioma.