MicroRNAs as biomarkers in malignant pleural mesothelioma

What is it about?

Abstract: Malignant pleural mesothelioma (MPM), a highly lethal cancer strictly related to asbestos exposure, is usually characterized by delayed diagnosis, resistance to current therapies, and dismal prognosis. MPM is difficult to distinguish histologically from nonmalignant reactive mesothelial proliferations (RMPs) as there are no clinically validated immunohistochemical markers yet and the main diagnostic criterion remains deep invasion into the pleura and underlying fat tissue, which is often not appreciable in small pleural biopsies. In this regard, microRNAs (miRNAs), given their size and stability, are particularly attractive biomarkers in formalin-fixed paraffin-embedded tissue specimens for routine pathology. Moreover, circulating miRNAs appear to be promising biomarkers for early detection and monitoring of patients with MPM. Here, we review the studies mostly performed by miRNA arrays and reverse transcription-quantitative polymerase chain reaction in formalin-fixed paraffin-embedded or frozen tissue samples, MPM cell lines, and blood/plasma/serum samples that have highlighted the potential of miRNAs as biomarkers in MPM. Certain studies have pointed to the ability of miRNAs to distinguish the different histological MPM subtypes or separate MPM from lung adenocarcinoma, and other investigations have revealed that miRNAs can aid in differentiating MPM from RMP or have prognostic value in predicting the patient outcome. Mechanistic aspects of the involvement of miRNAs in mesothelioma genesis and possible use of miRNAs as future therapeutic targets in MPM are also emphasized. Finally, limitations of the data currently obtained due to the drawbacks of reverse transcription-quantitative polymerase chain reaction, heterogeneity of MPM tissue samples, and differences in methodological platforms as well as in types of specimens utilized in different studies are discussed. Because of these inherent weaknesses of collected data, further studies assessing the expression and distribution of miRNAs by in situ hybridization in combination with the codetection of their respective targets by immunohistochemistry and further validation of miRNAs’ targets in vitro are warranted to fully reveal the potential clinical utility of miRNAs in MPM.

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Why is it important?

This review article summarizes the current status for research on microRNAs (miRNAs) as very promising diagnostic, prognostic, and possibly predictive (of therapeutic response) biomarkers in malignant pleural mesothelioma (MPM), an extremely lethal, difficult to diagnose cancer type. Deregulated miRNAs detected in tissue specimens or circulating in blood and that can distinguish the histological subtypes of MPM, differentiate MPM from other cancer types, aid in the challenging differential diagnosis of MPM vs. nonmalignant reactive mesothelial proliferation (RMP), or that have displayed prognostic significance for MPM patients are described. Furthermore critical evaluation of the current limitations and possible new applications of miRNAs in MPM diagnostics is presented.

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