**Abstract**

Extracellular vesicles are membrane-derived nanoparticles that represent a novel mechanism of cell-to-cell communication. It is well reported that EVs play a central role in the tumor microenvironment by mediating intercellular signaling among cancer cells. This has resulted in the development of therapeutic strategies targeting various EV signaling pathways in cancer. However, because of their small size and endogenous origin, they have been extensively explored for cancer drug delivery. Hence, owing to their natural ability to mediate intercellular communication, high stability, and low immunogenicity, they have emerged as an attractive platform for cancer treatment. However, limited production and insufficient loading with therapeutic moieties are some of the issues constraining their clinical translation. In this chapter, recent research studies performed in an attempt to develop EVs as cancer biomarkers or drug delivery systems will be discussed. Further, it will also discuss various strategies such as direct and indirect cell surface modification, which can be employed to make EVs successful as cancer therapeutics. Furthermore, it will highlight the current and completed clinical trials using naturally derived EVs as cancer therapeutics.

**Keywords:** breast cancer, extracellular vesicles, engineering, drug delivery, biomarker
