Prostate cancer frequently metastasizes and spreads to bone, causing severe pain, fractures, and other complications. The mechanisms that allow cancer cells to modify bone remodeling are incompletely understood. Researchers have now identified a microRNA, miR-940, that is abundant in exosomes secreted by prostate cancer cells and can trigger bone-forming lesions in mice. The findings indicate that microRNAs play a key role in bone metastatic environment and suggest potential novel therapeutic targets for bone metastasis.