Researchers say they have identified a switch that makes dormant breast cancer cells that have traveled to the lungs swell to lethal proportions—completing the dreaded process of metastasis or cancer spread. A team from Cold Spring Harbor Laboratory in Long Island, N.Y., reports that it staved off full-blown metastasis in mice by preventing mini-tumors in the lungs from recruiting stem cells called endothelial progenitors, which assemble into blood vessels to nourish the malignancy. Researchers do not know if the same thing would work for other types of cancer or cancer cells lodged in other body organs. Still, they hope to...