Tumor-derived extracellular vesicles (EVs) are reported to contain nucleic acids, including DNA. Several studies have highlighted the potential of EV-derived DNA (evDNA) as a circulating biomarker, even demonstrating that evDNA can outperform cell-free DNA (cfDNA) in terms of sensitivity. Researchers at Stavanger University Hospital have evaluated EVs as a potential source of tumor-derived DNA in patients with advanced pancreatic cancer. evDNA from both DNase-treated and untreated EV samples was analyzed to determine whether the DNA was primarily located internally or outside (surface-bound) the EVs. To assess whether methodology affected the results, the researchers isolated EVs using four different methods for small EV isolation and differential centrifugation for isolating large EVs. Their results indicated that the DNA content of EVs was significantly less than the cfDNA content isolated from the same plasma volume (p < 0.001). Most of the detected evDNA was also located on the outside of the vesicles. Furthermore, the fraction of tumor-derived DNA in EVs was similar to that found in cfDNA. In conclusion, these results suggest that quantification of evDNA, as a source of tumor-derived DNA, does not add information to that obtained with cfDNA, at least not in patients with advanced pancreatic cancer.
Schematic overview of methods used for isolating EVs
Plasma, clarified by differential centrifugation and filtration using a 0.8-μm membrane filter, served as input for each isolation method. lEVs were co-isolated after differential centrifugation of plasma and before plasma filtration. TEI: total exosome isolation; lEVs: large extracellular vesicles.