Abstract

In 2018, there were an estimated 8.6 million new cases of cancer in women and 4.2 million deaths from cancer worldwide. In addition, 20% of women who are diagnosed with breast cancer will go on to develop metastases. Therefore, there is an urgent need to discover new molecular markers for the diagnosis and prognostic prediction of metastatic illness and to create novel treatment agents. MicroRNAs (miRNAs) have been studied extensively in breast cancer and have been shown to induce numerous alterations in the expression of genes involved in carcinogenesis. In this review, we compile recent information on breast cancer-specific miRNA expression profiles and their role in regulating invasive processes, in conjunction with alterations in cytoskeletal structure, cell-cell adhesion junctions, cancer cell-extracellular matrix interactions, tumor microenvironments, epithelial-to-mesenchymal transitions, and cancer cell stem abilities. Finally, we discussed the role of miRNA isoforms and exosome-mediated miRNA transfer in cancer invasiveness, and we focused on how epigenetic regulation affects individual miRNAs and how those miRNAs interact with other regulatory genes. While more work is needed to fully understand the role of miRNAs in cancer, the findings presented here help advance the treatment of metastatic disease.