Evaluation of: Valastyan S, Reinhardt F, Benaich N et al.: A pleiotropically acting microRNA, miR-31, inhibits breast cancer metastasis. Cell 137(6), 1032-1046 (2009). Several microRNAs (miRNAs) regulate various steps of the metastatic cascade; however, they typically regulate both metastasis-related genes and genes involved in proliferation, cell-cycle regulation or apoptosis. miR-31 was determined to regulate a number of metastasis-related genes in breast cancer cells and tissues. Using a variety of approaches, it was demonstrated that cellular levels of miR-31 correlated with the cell's ability to invade and metastasize; cells with increased levels of the miRNA were less metastatic. These studies were extended to patient's tissues, demonstrating that breast cancer patients with higher miR-31 expression, or lower expression of the miR-31 target genes, had prolonged survival. A miRNA that works pleiotropically to regulate invasion and metastasis has been identified, suggesting a new pathway for therapeutic intervention of metastasis in breast cancer.