Imagine this kind of warning on a cigarette package: Quitting smoking now greatly reduces serious risk to your health, particularly if your DNA is mutated at the 15q24 locus. Would you get tested for this mutation?

Right now, there is no such test. But someday, there might be.

Years of study and a mountain of evidence point to tobacco smoking as the single most important risk factor for lung cancer. Nonsmokers (people who have smoked fewer than 100 cigarettes over the course of their lives) have less than a 1% chance of ever developing lung cancer…