MicroRNAs in Breast Cancer: Diagnostic and Prognostic Potential, Challenges, and Clinical Reliability

Despite the rise in precision medicine, breast cancer management still lacks the non-invasive tools necessary to track tumor dynamics in real time. MicroRNAs (miRNAs) have emerged as strong candidates to fill this gap, particularly within the liquid biopsy framework. Their inherent stability in circulation and their ability to reflect specific molecular changes make them compelling biomarkers for clinical use. This review outlines the current state of miRNA research in breast cancer, specifically assessing their utility in early diagnosis and the prediction of patient outcomes. The focus is on a range of high-priority targets, such as miR-21, miR-155, and the miR-200 family, which have demonstrated consistent dysregulation across different molecular subtypes of breast cancer. These molecules offer a distinct advantage over traditional protein markers by providing a more precise look at tumor progression and therapeutic resistance. However, the transition from discovery to clinical practice remains blocked by technical inconsistencies. The lack of standardized protocols for RNA isolation and the difficulty in identifying reliable reference genes for normalization continue to affect reproducibility. While the potential for these biomarkers is well-documented, the field must now shift its focus toward establishing clinical reliability. Large-scale prospective validation studies are on the horizon to facilitate this implementation. All in all, international consortia and multi-center trials are required to test circulating miRNA biomarkers in real-world settings, ensuring they are feasible enough to guide routine oncological decision-making.