Scientists have discovered why breast cancer cells that have spread to the lungs may "wake up" following years of sleep, forming incurable secondary tumors. Their research reveals the mechanism that triggers this breast cancer "time bomb"—and suggests a strategy to defuse it. Patients with estrogen receptor positive (ER+) breast cancer—the most common type—have a continued risk of their cancer recurring in another part of their body for many years or even decades after their original diagnosis and treatment. When breast cancer cells spread from the first cancer in the breast to other parts of the body it is called secondary...