If cancer can be stopped once it has spread, lives will be saved. A small section of R.N.A. seems effective at killing breast cancer cells. "A tiny snippet of R.N.A. called microRNA-31 or miR-31 can kill breast cancer cells that have spread to the lungs. The microRNA turns off production of proteins that cells use to build skeletons and cling to each other, researchers at M.I.T. and the Whitehead Institute in Cambridge, Massachusetts, show in a paper published in the March 15 Genes & Development. The microRNA didn’t affect the initial tumor. Therapies that can stop cancer once it has spread may eliminate up to 90 percent of cancer deaths."