The exosomal nature of extracellular vesicles derived from the blood of animals and a canine tumor cell line was shown by the size distribution in the range of 50–100 nm, as measured by dynamic light scattering, and by the presence of typical exosomal surface markers such as the tetraspanines CD9, CD63, and Hsp70. The gene discussed is CD9; the disease is neoplasm.