**6. Exosomes for drug delivery in breast cancer: progress and future promise**

Although exosomes have been shown to mediate cancer development, they are an emerging platform for drug delivery to cancerous sites because of their excellent biocompatibility, low immunogenicity (since they are derived from the patient's own cells), good tolerance, and remarkable biodistribution. Owing to their small size, they can readily pass through different bodily barriers such as the blood-brain barrier [61]. Compared to synthetic nanoparticles, exosomes are relatively easy to manipulate through surface modification in order to enhance their targeting efficiency to cancer cells. Recently, the use of exosomes for drug delivery in breast cancer cells has been proven to be efficient. Alvarez-Erviti et al. delivered the chemotherapeutic drug doxorubicin to breast cancer tissues in a mouse model [62]. First, they engineered these cells by expressing Lamp2b, a lysosome-associated membrane glycoprotein 2b, on their surface and fused with a targeting peptide for integrins. They then isolated
