A particular microRNA (a small regulatory molecule) can cause tumors to metastasize, according to a recent study by scientists at the Whitehead Institute for Biomedical Research, in Cambridge, Mass (Ma L et al. Nature. doi: 10.1038/nature06174 [published online ahead of print September 26, 2007]). They found that this molecule, called microRNA-10b, is found in much higher levels in metastatic cancer cells than in nonmetastatic cancer cells. In addition, inserting extra copies of the microRNA into nonmetastatic human breast cancer cells forces the cells to become metastatic when injected into the mammary fat pads of mice.
Hampton T. MicroRNA and Metastasis. JAMA. 2007;298(17):1998. doi:10.1001/jama.298.17.1998-a