Exosome-mediated drug resistance in cancer: the near future is here

Drug resistance exerts a crucial role in several cancer treatments. Understanding the resistance mechanisms against different therapeutic agents can be helpful to determine the prognosis, but remains a tricky task. In this context, tumor-derived exosomes (TDEs) may give crucial answers about these resistance mechanisms. Exosomes are biological nanovesicles with an average size around 30–100 nm of diameter (Figure 1) that originate from the endocytic pathway by the inward budding of multivesicular bodies (MVB), and they function as cell-free messengers, involved in the cell–cell communication [Kowal et al. 2014]. It has been demonstrated that both cells in physiological and pathological conditions release exosomes and that exosomes are easily detected in several body fluids, such as plasma, serum, urine, saliva, etc. [Rolfo et al. 2014]. It has been demonstrated that TDEs contain different proteins, lipids, mRNAs and miRNAs and have pleiotropic functions in the tumor microenvironment, tumor growth and progression, immune escape, angiogenesis, invasion, and drug resistance [Kowal et al. 2014; Rolfo et al. 2014; Fontana et al. 2013].