This question is on the mind of nearly every cancer patient, and their families. What exactly is cancer and why does it occur in some people, but not others? Is it just the luck of the draw, or are there genetic, lifestyle, dietary and environmental factors that are responsible? And if so, how important and controllable are they? This talk addresses these basic questions, attempting to put into perspective what scientists know - and don’t know - about the causes of cancer, and what individuals can do to lower their risk. From the Series:Science Forum