The expanding role of exosomes in cancer biology and therapy

The role of extracellular vesicles, of which exosomes is one type, in oncogenesis continues to be defined. Normal human blood is estimated to contain about 2,000 trillion exosomes, and the blood of cancer patients is estimated to contain about 4,000 trillion exosomes (1). Virtually all cell types appear able to produce exosomes. Exosomes are heterogeneous, and heterogeneity appears enhanced in cancer (1). Exosomes provide a means of intercellular communication for both normal and malignant cells. Since exosomes are detected in many body fluids, including urine, semen, saliva, amniotic fluid, cerebrospinal fluid, bile, ascites, tears, breast milk and blood, they have been reported as a potentially useful liquid biopsy for cancer detection (1). Tumor cells use exosomes to promote their survival and growth (2).