A novel imaging-based approach for large extracellular vesicle detection and prognostic stratification in metastatic breast cancer

Background Large extracellular vesicles (LEVs) are membrane-bound extracellular particles released by tumour cells into body fluids. Circulating LEVs carry tumour-associated biomaterials and are more abundant than circulating tumour cells (CTCs), representing a valuable liquid biopsy analyte. We evaluated the RareCyte® CTC platform's ability to identify LEVs in blood smears and explored associations with clinicopathological features in a metastatic breast cancer (MBC) cohort.Methods MBC patient samples (N = 72) from a previously published prospective comparison study were retrospectively re-analysed to develop and validate an LEV identification and enumeration workflow. Correlations with CellSearch® tumour-derived extracellular vesicle (tdEV) counts and CTC counts were assessed using Spearman's rho. Between-platform comparisons were performed using Wilcoxon's signed-rank test Associations with overall survival (OS) were assessed using Kaplan-Meier analysis and Cox proportional hazards models. Overall survival was defined as the interval between blood collection and death from any cause.Results Median LEV count [IQR] was 89 [53-208], with detectable LEVs in patients with low or absent CTC counts. LEV counts positively correlated with matched CTC counts (Spearman's ρ = 0.88, p Conclusion We developed an operational workflow for LEV detection and quantification using the RareCyte® CTC analysis platform. The inclusion of LEVs into CTC-based liquid biopsy analyses may provide complementary biomarker information, particularly in patients with low CTC burden.