A little more than a dozen years ago two researchers came up with a way of thinking about how tumors grow that changed the way most of the scientific community considered the hundred or more different diseases we call cancer. The varied and complex ways that normal cells become malignant, Douglas Hanahan and Robert Weinberg famously wrote in 2000, could be divided into six main steps--ranging from dividing uncontrollably to avoiding self-destruction. Developing treatments that targeted those essential processes should make cancer therapy much more predictable and effective, they argued.