Exosomes are a subtype of vesicles released by cells of both healthy and 
neoplastic origin. Preclinical studies suggest a role for tumour-derived 
exosomes in tumour progression, mainly through the transfer of RNA and proteins 
from tumour cells to other cells. The transfer of RNA and proteins by 
tumour-derived exosomes seems to mediate stimulation of angiogenesis and 
suppression of immune cells; in contrast, exosomes from healthy cells of the 
immune system appear to have anti-tumour characteristics. Characterisation of 
the RNA or protein profile of tumour-derived exosomes could have diagnostic or 
prognostic value, for example, in brain tumours. Anti-tumour therapies could be 
based on exosomes, for example, by blocking the formation of tumour-derived 
exosomes or having exosomes release therapeutic agents at specific sites. The 
most advanced application of this is the use of exosomes from dendritic cells in 
tumour vaccination; the safety of this has been demonstrated in phase I studies.