Extracellular vesicle-derived protein biomarkers for breast Cancer diagnosis: a systematic review, meta-analysis, and...

Extracellular vesicle (EV)-derived proteins are increasingly investigated as liquid biopsy biomarkers because they can reflect tumour-associated molecular processes in clinically accessible biofluids. However, their diagnostic performance and methodological robustness in breast cancer remain incompletely defined. This study evaluated EV-derived protein biomarkers for breast cancer diagnosis through a systematic review and meta-analysis of primary studies, complemented by an umbrella review of published systematic reviews and meta-analyses. A structured search was conducted in PubMed/MEDLINE, Web of Science, and Scopus from database inception to February 2026 and subsequently updated during revision. Primary studies assessing EV-derived proteins or proteomic signatures in clinically relevant biofluids and reporting diagnostic performance metrics were eligible for quantitative synthesis. Methodological quality was assessed using QUADAS-2, and the quality of secondary reviews was evaluated with AMSTAR 2. Six independent studies were included in the meta-analysis. The pooled area under the receiver operating characteristic curve was 0.90 (95% CI 0.86-0.94), indicating high discriminatory capacity. However, the estimate should be interpreted cautiously because of the limited number of studies and substantial heterogeneity (I² = 84.6%). The umbrella review identified four main functional domains: diagnostic applications, therapeutic resistance, tumour progression and metastasis, and global proteomic characterisation. EV-derived protein biomarkers show potential for breast cancer diagnosis, but current evidence is limited by methodological heterogeneity, incomplete analytical standardisation, and the lack of clinically actionable thresholds. Future progress will depend on harmonised pre-analytical and analytical protocols, multicentre validation, and diagnostic frameworks supporting their potential implementation in clinical laboratory practice.