Exosomes are nanovesicles secreted into the extracellular environment upon 
internal vesicle fusion with the plasma membrane. The molecular content of 
exosomes is a fingerprint of the releasing cell type and of its status. For this 
reason, and because they are released in easily accessible body fluids such as 
blood and urine, they represent a precious biomedical tool. A growing body of 
evidence suggests that exosomes may be used as biomarkers for the diagnosis and 
prognosis of malignant tumors. This article focuses on the exploitation of 
exosomes as diagnostic tools for human tumors and discusses possible 
applications of the same strategies to other pathologies, such as 
neurodegenerative diseases.