Stopping breast cancer from spreading is the fierce hope of every woman with the disease. Even better would be to detect and stop the metastasis before it actually progressed. Jiang Yang, Marsha Moses and colleagues made a set of discoveries that could help turn that hope into reality. They found that the protein lipocalin 2 (Lcn2) promotes breast cancer metastasis and that it does so by inducing a key pathological event, the epithelial to mesenchymal transition. In addition, elevated levels of Lcn2 were detected in the urine of women with metastatic breast cancer. The discovery suggests the protein may have potential as a marker for a noninvasive method of diagnosing advanced breast cancer and as a target for future metastasis-thwarting therapies. Yang, an HMS research fellow in surgery, and Moses, an HMS professor of surgery, both at Children’s Hospital Boston, and colleagues reported the findings online Feb. 23 in Proceedings of the National Academy of Sciences.