The more scientists learn about microRNAs -- short strands of RNA that can interfere with normal gene activity -- the more obvious it becomes how closely they are associated with cancer. In a new study, scientists at The Wistar Institute and their colleagues have identified two microRNAs (miRNAs) that promote tumors’ deadly spread, or metastasis. One of the miRNAs may provide an early warning of metastatic breast cancer and the need for aggressive treatment.