MicroRNA-21 (miR-21) overexpression is associated with the development and progression of MDR in breast cancer, and it is emerging as a novel and promising MDR-reversing target.
MiR-21 has a relatively high diagnostic value for detecting breast cancer, and miR-21 assays based on plasma, serum, and tissue achieved relatively higher accuracy.
miR-21 (<i>p</i> < 0.001), miR-23b (<i>p</i> = 0.033), miR-200b (<i>p</i> < 0.001) and miR-200c (<i>p</i> < 0.001) expression was higher in metastatic compared to early breast cancer.
microRNA-21 was up-regulated in HER2 positive and Basal-like breast cancer types, while microRNA-206 was up-regulated in Luminal A and B types of breast cancer. microRNA-21 expression negatively correlated with the level of ER and PR but positively correlated with HER2 expression and tumor malignancy, while microRNA-206 showed the opposite trend.
Additionally, the expression level of miR-21 in human breast cancer cell (MCF-7) lysate is successfully measured, suggesting its potential in clinical diagnosis.
Adoptive cell-transfer assay further showed that silencing of miR-21 could alter the enrichment of CCR6(+) Tregs in the tumor mass and endow effectively antitumor effect of CD8(+) T cells using a murine breast cancer model.
Also, it is important to indicate that some exosomal miRNAs including miR-126, miR-122, miR-92-1, miR-19a, and miR-29c together with circular miRNAs, such as miR-21-5p, miR-96-5p, and miR-125b-5p can provide a promising evaluation route in breast cancer prognosis.
As a proof of concept, the simultaneous detection of two breast cancer-related MicroRNAs (miR-21 and let-7a miRNA) has been achieved with total internal reflection fluorescence (TIRF)-based imaging and the detection sensitivity of our method has been demonstrated to be improved by at least two orders of magnitude compared with conventional AgNC-MBs.
Based on this preliminary study, we suggest that these miRNAs, especially let7a and miRNA21, might be useful markers in follow-up of breast cancer and in prognosis.