How can someone get lung cancer who has never smoked?

Dumb luck: Second-hand smoke, usually from the spouse's habit, kills a few thousand people yearly in the us. There are two genetic types of lung cancer that seem to pop up fairly often in non-smokers; they've been known for a few decades and now it's clear they have a different and distinctive biology and often respond to some of the very new easy treatments.

We don't know: Although smoking is by far the greatest risk factor for lung cancer, not every lung cancer patient has a smoking history. Some non-smokers have other risks like second hand smoke or asbestos exposure. But a growing number have no risk factors that we know of. Unfortunately the lack if cigarette exposure does not completely rule out the possibility of lung cancer.

Concur: Agree with drevans and others. Would further add, unfortunate reality is that the most afflicted group of non-smokers are actually women. We do not know why women are the most often afflicted within the non-smoker lung cancer victims. It is a tragedy and important health issue.