Comparison of cell-free and small extracellular-vesicle-associated DNA by sequencing plasma of lung cancer patients

Blood contains multiple analytes that can be used as liquid biopsy to analyze cancer. Mutations have been detected in DNA associated with small extracellular vesicles (sEVs). The genome-wide composition and structure of sEV DNA remains poorly characterized, and whether sEVs are enriched in tumor signal compared to cell-free DNA (cfDNA) is unclear. Here, using whole-genome sequencing from lung cancer patients we determined that the tumor fraction and heterogeneity are comparable between DNA associated with sEV (<200 nm) and matched plasma cfDNA. sEV DNA, obtained with size-exclusion chromatography, is composed of short ∼150–180 bp fragments and long >1000 bp fragments poor in tumor signal. The structural patterns of sEV DNA are related to plasma cfDNA. Mitochondrial DNA is relatively enriched in the sEV fractions. Our results suggest that DNA associated to sEV (including exosomes) is not preferentially enriched in tumor signal and is less abundant than cfDNA.