The goal of this study is to use a proteomic approach to understand the roles of the ESCRTIII-VPS4 complex in the formation of multiple vesicular body (MVB)-dependent exosomes. Results from our study suggest that attenuation of the expression of VPS4, an AAA+ ATPase, can alter the content of exosomes that are secreted by breast cancer cells and render them resistant to chemotoxins. Mostly importantly, we have also found that this aberrant VPS4-mediated MVB dysfunction is often associated with high grade and recurrent tumors. We will discuss the pathological consequences of this VPS4-mediated alternative exosome secretion and its potential impact on biomarker discovery.