Scientists have identified four potential biomarkers that may help resolve the difficult differential diagnosis between malignant pleural mesothelioma (MPM) and non-malignant pleural tissue with reactive mesothelial proliferations (RMPs). This is a frequent differential diagnostic problem in pleural biopsy samples taken from patients with clinical suspicion of MPM. The ability to make more accurate diagnoses earlier may facilitate improved patient outcomes. This new study appears in the Journal of Molecular Diagnostics.
“Our goal was to identify microRNAs (miRNAs) that can aid in the differential diagnosis of MPM from RMPs,” says lead investigator Dr Eric Santoni-Rugiu of the Laboratory of Molecular Pathology at the Department of Pathology of Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark. MiRNAs, which are small, non-coding RNA strands composed of approximately 22 nucleotides, have been shown to be potential diagnostic, prognostic, and predictive markers in other cancers.
Diagnostic potential of miRNAs
After screening 742 miRNAs, the investigators identified miR-126, miR-143, miR-145, and miR-652 as the best candidates to diagnose MPM. Using results from these four miRNAs, tissue samples from patients with known outcomes could be classified as MPM or non-malignant with an accuracy of 0.94, sensitivity of 0.95, and specificity of 0.93. Further, an association between miRNA levels and patient survival could be made.
“The International Mesothelioma Interest Group (IMIG) recommends that a diagnostic marker of MPM have sensitivity/specificity of >0.80, and these criteria are fulfilled by our miRNA classifier,” comments Dr Santoni-Rugiu. The authors suggest that diagnostic accuracy can be further improved by adding immunohistochemical testing of miRNA targets in biopsy tissue to their miRNA assay. This combined assay could enable analysis of samples with low tumour cell count.
Distinguishing MPM from non-malignant abnormalities, such as reactive mesothelial hyperplasia or fibrous pleurisy (organising pleuritis), can be challenging as there are no generally accepted diagnostic biomarkers for differentiating these two conditions. As a result, patients often present with the disease when they are already at an advanced stage, and less than 20% of patients can be successfully treated surgically.
For immunohistochemistry, FFPE tissue sections underwent staining using antibodies to the known miR-126 targets. LAT1 and Crk-II were evaluated by light microscopy and scored by a semiquantitative H score. Although no significant differences were found between MPM and non-malignant samples for Crk-II, the MPM samples had a median H score of 2 for LAT1 immunostaining, which was significantly higher than the 0.5 median score for the non-malignant samples (p < 0.01). Furthermore, the level of LAT1 in MPM inversely correlated with that of miRNA-126.
The authors concluded that overall, these results indicate that these four miRNAs may be suitable biomarkers for distinguishing MPM from RMPs. If further validated, the combination of immunohistochemistry for miRNAs with immunohistochemical testing of miRNA targets may therefore have the potential to aid in the diagnosis, and thus outcome, of MPM.