A Journal of Translational Medicine study showed tumor-derived exosomal miR-221-3p enhances breast cancer metastasis to the brain by reprogramming the brain microenvironment and supporting tumor cell colonization. The team traced miR-221-3p transfer to recipient brain cells and tied its activity to pathways that promote invasion and survival. Targeting exosomal miRNA release or uptake may present a therapeutic avenue to block metastatic seeding.