Exosomes are small membrane-bound vesicles that in recent years have emerged as important molecules for inter-cellular communication. Exosomes are produced during both normal and patho/physiological conditions, and cancer cells have been shown to secrete exosomes in greater amounts than normal cells. CD9 is a 24 kD type III transmembrane protein. It is a member of the tetraspan family (spanning the membrane four times) found on platelets, B cell progenitors, activated lymphocytes, granulocytes, endothelial cells and epithelial cells. CD9 is also abundant in exosomes embranes.