In multicellular organisms, communication between cells involves secretion of proteins that bind to receptors on neighboring cells. While this has been well documented, another mode of intercellular communication has recently become the subject of increasing interest: the release of exosomes. In cancer, tumor exosomes are involved in various aspects of pathogenesis, including proliferation, immunosuppression, and metastasis. Given the ability of exosomes to export unneeded endogenous molecules from cells, these structures hold great potential as anticancer therapeutic agents. They are also being studied as prognostic markers for cancer.