WASHINGTON – Scientists may have found a way to tell which smokers are at highest risk of developing lung cancer: measuring a telltale genetic change inside their windpipes.

A test based on the research is being developed in hopes of detecting this deadly cancer earlier, when it’s more treatable.

“They’re heading toward lung cancer, and we can identify them with this genomic test,” said Dr. Avrum Spira of Boston University School of Medicine, who led the research published Wednesday in the journal Science Translational Medicine.

Lung cancer – which killed nearly 160,000 Americans last year – is the leading cancer killer, and cigarette smoke is by far its main cause. Yet, not all smokers develop lung cancer; Spira cites estimates that 10 to 20 percent will. The risk depends in part on how much people smoke, for how long and how long ago they quit – but there’s no way to predict who will escape it and who will not.

“Even for people who have stopped smoking, there’s a significant risk of cancer down the road, and it would be nice to identify which patients are really at risk,” said Duke University lung cancer specialist Dr. Neal Ready.

Rather than focusing on the lung itself, Spira’s team took a different approach. Smoking bathes the entire respiratory tract in toxins. So he hunted for the earliest signs of impending lung cancer upstream, in how different genes are turned on and off inside the upper airway as the body tries to defend itself and those defenses weaken over time.

Sure enough, he found a genomic signature – a pattern of gene activity – in otherwise normal windpipes that distinguished some current or former smokers who had lung cancer from those who didn’t.