Abstract
Breast cancer remains a major global health burden, indicating the need for less invasive methods and more accurate biomarkers for diagnosis, prognosis, and treatment monitoring. Circulating microRNAs (miRNAs) are promising liquid biopsy biomarkers that can be detected in peripheral blood and may reflect tumor-associated molecular changes. This integrative literature review assessed recent evidence on circulating miRNAs in breast cancer, with emphasis on blood, plasma, and serum samples and their applications in diagnosis, prognosis, and treatment-related monitoring. The search was conducted for original studies published between 2024 and 2026. After screening and eligibility assessment, 44 studies were included. Serum was the most commonly analyzed sample, followed by plasma; RT-qPCR was the dominant detection method. Diagnostic applications were the most frequently reported, with miR-21 and miR-155 among the most consistently investigated biomarkers. Multi-miRNA panels and computational signatures generally showed higher diagnostic performance than individual miRNAs. Circulating miRNAs were also associated with disease stage, metastasis, recurrence, survival, and response to neoadjuvant chemotherapy, endocrine therapy, trastuzumab, and CDK4/6 inhibitors. Nonetheless, despite these promising findings, methodological heterogeneity, small sample sizes, inconsistent normalization strategies, and limited external validation remain barriers to clinical applications. Standardization and prospective multicenter validation are needed to establish clinical utility.