Breast cancer is a highly heterogeneous malignancy that remains one of the leading causes of cancer-related mortality among women worldwide. Despite significant advances in breast cancer research and therapy, disease heterogeneity, treatment resistance, and metastatic progression remain major obstacles to effective disease management. Among the molecular regulators involved in breast cancer, microRNAs (miRNAs) have been recognized as critical post-transcriptional regulators of gene expression, functioning as either oncogenes or tumor suppressors. By modulating the expression of target RNAs, miRNAs control key biological processes involved in tumor initiation and progression, including cell proliferation, apoptosis, angiogenesis, epithelial-mesenchymal transition (EMT), invasion, and metastasis. To investigate miRNA function and explore their therapeutic potential, a wide range of approaches have been developed to modulate miRNA expression. These include gain-of-function strategies, like miRNA mimics, miRNA expression vectors, and CRISPR activation (CRISPRa), as well as loss-of-function approaches, including anti-miRNA oligonucleotides (AMOs), miRNA sponges, CRISPR-Cas9-mediated gene knockout, and CRISPR interference (CRISPRi). This review provides a comprehensive overview of the biological roles of miRNAs in breast cancer and discusses current technologies for miRNA modulation, their molecular mechanisms, experimental and therapeutic applications, and associated limitations. In addition, it summarizes recent advances in miRNA delivery systems, including viral vectors, organic nanoparticles, and inorganic nanocarriers, highlighting their potential to improve delivery efficiency, target specificity, and facilitate clinical translation. Finally, the review discusses future perspectives, emphasizing the transition from single-target interventions toward network-level regulation and the integration of miRNA-based strategies into precision oncology to support the development of more effective breast cancer therapies.
