**1. Introduction**

20 Advances in Cancer Therapy

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Cancer, a leading cause of death globally, is projected to become more prevalent in coming years due to increasing life expectancy. Among possible treatment options, the use of biomarkers especially has shown great potential as a gateway to personalized medicine, and in turn, great promise for improved diagnosis, prognosis and treatment of cancer and other diseases. However, the use of biomarkers in cancer therapeutics has thus far exhibited mild success, at best. The most common tool used for biomarker discovery is plasma proteomics due to the accessibility of blood samples and the rapid development of highly sensitive proteomics technologies. However, other body fluids such as urine may also be a reservoir for important marker proteins.

Extracellular membrane vesicles ranging in diameter of 30-1000 nm and originating from various cellular origins have been increasingly recognized for their participation in a variety of both normal and pathological cellular processes. Regardless of their cell type of origin these membrane bound vesicles or exosomes provide a protected and controlled internal microenvironment outside the cell for metabolic objectives of the host cell to be carried out at a distance from the host cell. They are also believed to be instrumental in cell-cell and cellextracellular communication. Moreover, while knowledge of exosome biogenesis and physiological relevance remains limited, accumulating evidence suggests that their bioactivity may be clinically applicable in cancer therapeutics. One recent work suggests that the use of exosomes in immunotherapy may prime the immune system to recognize and kill cancer cells and thus could form a viable basis for the development of novel cancer vaccines.

This chapter will review current knowledge pertaining to exosomes, describe possible uses of exosomes in immunotherapy, and address challenges and future directions in bringing exosome-based cancer vaccines or immunotherapies closer to clinical reality.
