The Role of cfDNA in Early Diagnosis and Treatment Management of Breast Cancer: Implementation Challenges and Opportunities in Southeast Asia

Background: Breast cancer is the most common malignancy among women worldwide and a growing public-health challenge in Southeast Asia. Mammography has reduced sensitivity in many Asian populations because of a high prevalence of dense breast tissue and an earlier peak age of onset. Circulating cell-free DNA (cfDNA) and circulating tumour DNA (ctDNA) have emerged as non-invasive biomarkers for detection, monitoring and precision management. Objective: To synthesise current evidence on cfDNA applications across the breast-cancer care continuum, and to appraise opportunities and implementation challenges in Southeast Asia, while distinguishing analytical validity, diagnostic accuracy and clinical utility. Methods: We conducted a non-systematic narrative review of English-language literature (2010-2025) from PubMed/MEDLINE, Scopus, Web of Science and Google Scholar, supplemented by regional reports, using terms combining cfDNA/ctDNA/liquid biopsy with breast cancer and Southeast Asian country names. Evidence was organised using the analytical validity-clinical validity-clinical utility framework, and breast-specific findings were separated from multi-cancer assay results. Results: Multi-omics cfDNA assays integrating genomic, epigenetic and fragmentomic features show high specificity and promising, stage-dependent sensitivity for early detection; several key performance estimates, however, derive from multi-cancer rather than breast-specific cohorts. ctDNA supports response monitoring, minimal-residual-disease detection and resistance identification, but most regional evidence is prognostic rather than interventional, and outcome benefit from acting earlier remains largely unproven. Regional evidence is concentrated in Vietnam and Thailand. Clonal haematopoiesis, low ctDNA shedding in early disease and pre-analytical variation remain important error sources. Conclusion: cfDNA-based liquid biopsy is a promising adjunct that should currently complement, not replace, established breast-imaging pathways. Realising its potential in Southeast Asia will require locally generated evidence and coordinated action on cost, infrastructure, regulation and equity.