Lung cancer is a strange one. As smoking levels drop, in some populations one can say that "most" lung cancer has nothing to do with smoking. So the doc has 10 patients with lung cancer, but only one of them is a smoker. With such numbers is gets hard to say that smoking was the cause. It was easy when the same doc had 30 patients and 21 were smokers, but times change. Statistics are hard and need to be revisited regularly.