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. TSG101, a 46 kDa protein, is the product of a recently identifed Tumor Susceptibility Gene whose inactivation in mouse fibroblasts results in cell transformation and the ability of those cells to form tumors in nude mice. TSG101 is highly expressed internally to EVs and it is considered one of the common markers for exosome detection.