Salivary miRNA-21 expression as a potential non-invasive diagnostic biomarker in breast cancer

Breast cancer (BC) is the most common neoplasm and the most important cause of mortality in women worldwide. microRNAs (miRNAs) are single-stranded RNA molecules with approximately 22 nucleotides in length and act as regulators of eukaryotic gene expression by targeting various mRNAs. In the present study, we evaluated the expression level of miR-21 in saliva samples of BC patients compared to controls to introduce as a novel diagnostic biomarker. Salivary samples were collected from 41 patients with BC and 39 healthy individuals. The salivary expression of miR-21 was investigated using quantitative reverse-transcription polymerase chain reaction (RT-qPCR). The receiver operating characteristic (ROC) curve analysis was applied to evaluate the potential role of salivary miR-21 as a diagnostic biomarker in BC patients. Further, to predict the possible molecular mechanisms of miR-21 during BC development, in silico analysis was applied to enrich the signaling pathways in which miR-21 may be involved. It was shown that the miR-21 expression level in the BC group's saliva samples was significantly upregulated relative to the control group. Also, 100% sensitivity and 100% specificity were shown for this potential biomarker, according to which the area under the curve is equal to one, which indicates the high diagnostic value of this biomarker. Finally, MAPK signaling pathway was suggested as a potential pathway involved in BC development. According to the results, the expression level of miR-21 in BC patients' saliva samples could be considered a novel diagnostic biomarker in BC patients.