Aberrant miRNA promoter methylation and EMT‐involving miRNAs in breast cancer metastasis: Diagnosis and therapeutic implications

Breast cancer (BC) is the most prevalent cancer in women worldwide. Although extensive studies are ongoing concerning its intricate molecular mechanisms, development of novel therapies and more accurate diagnostic and prognostic approaches is still a challenge. Epithelial–mesenchymal transition (EMT) enables the invasion of metastatic cancer cells and has recently been highlighted in a Cancer Stem Cell (CSC) model of BC. Epigenetic events as well as miRNA expression are the master regulators of tumorigenesis and add a further layer to the complexity of BC pathogenesis. The miRNAs are related to epigenetic event and additionally affect epigenetic pathways. Recent evidence demonstrates that epigenetic mechanisms such as DNA methylation may control miRNA expression. Because each miRNA may regulate several target genes, dysregulation of miRNA caused by aberrant DNA methylation patterns of the locus may influence important downstream pathways. Furthermore, some miRNAs is believed to regulate important DNA methylator factors. Any disruption or modification of this intricate network can contribute to the disease process; thus, it is essential to understand these changes. Advancements in new sequencing technologies to detect DNA methylation patterns has provided the opportunity to determine differentially methylated regions (DMRs) of the miRNA locus and their effect on expression profiles to improve BC diagnosis and treatment. The current review examines the interplay of DNA methylation mechanisms and miRNA function in invasive tumorigenesis, specifically EMT and CSC of BC, to highlight its potential for advancements on BC etiology, diagnosis, and therapy.