Exosomes are tiny vesicles released from cells that carry proteins, lipids, and nucleic acids: cargo that can affect the biology of recipient cells. In a Perspective, Anastasiadou and Slack highlight recent studies that reveal how these vesicles act as vehicles to spread cancer. Exosomes that are released by cancer cells harbor oncogenic microRNAs (miRNAs), proteins involved in miRNA biogenesis, and miRNAs that induce inflammatory conditions that support tumor growth and metastasis. Such cancer exosomes cause normal cells to form tumors in animal studies. The findings could guide the development of exosome-based diagnostics and therapies for cancer….