In the fall of 2006, a new machine arrived at what’s now known as the Genome Institute at Washington University in St. Louis. It was capable of reading DNA a thousand times as quickly as the facility’s earlier machines, and at far less cost. Elaine Mardis, the center’s codirector, immediately began using it to sequence cancer tissues, scouring their DNA for mutations. Just five years later, Mardis and her collaborators have sequenced both cancerous and healthy tissue from several hundred patients and identified tens of thousands of mutations. Some of the findings have led to new approaches to treating cancer, while others have opened new avenues of research.