Genetics May Increase Smokers' Lung Cancer Risk

Scientists conducting genome-wide association studies have found a region on chromosome 15 associated with the development of lung cancer. The studies may help to explain why some smokers get lung cancer and others don't.

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If there is one thing that medical science has proven for sure, it's that there's a link between smoking and lung cancer. That said, scientists still don't understand the nature of that link and why some smokers get lung cancer and others don't.

NPR's Joe Palca reports on three papers that'll be published tomorrow to explore that question.

JOE PALCA: One of the hottest new techniques in genetics is something called a genome-wide association study. Basically, you take DNA from thousands or even tens of thousands of people and look for genetic differences between people who have a disease and those who don't.

The differences show up in what are called markers. These are places along the chromosomes that vary among the individuals - think of flags along the railroad track. Finding a marker associated with a disease indicates you may be near a gene that's involved in that disease. Since we inherit one chromosome from each of our parents, each marker comes in two copies.

Chris Amos led one of the three association studies being published in the journals Nature and Nature Genetics. He's at the M.D. Anderson Cancer Center in Houston. Amos says his group found a marker on chromosome 15 that was clearly associated with lung cancer. If you inherited one particular copy of this marker, your risk of lung cancer went up 28 percent.

Professor CHRISTOPHER AMOS (Epidemiology, M.D. Anderson Cancer Center, Houston): And if you have two copies of the markers, then you're at about 80 percent increased risk over someone that have no copies of these variants.

PALCA: Amos says the two other studies - one from France and the other from Iceland - found nearly the exact same thing. Now, this region of chromosome 15 where the marker sits is home to several genes that control the way the body responds to nicotine.

Mr. AMOS: So the presumption now is that nicotine itself or metabolite of nicotine is increasing one's risk for having lung cancer.

PALCA: Amos says it's still not clear exactly what the role of smoking is. The study from Iceland seemed to show that only people who had the marker and smoked were at higher risk of lung cancer. But the French group's data showed that it was the marker alone that increase risk regardless of whether someone smoke or not. The Houston group's data was somewhere in the middle.

Harvard Medical School's David Hunter says this discrepancy is one of the reasons the results should not yet be used to assess cancer risk for individual smokers. Hunter says it would be a huge mistake to think you were protected from lung cancer if you didn't have this particular marker.

Dr. DAVID HUNTER (Ophthalmology, Harvard Medical School): And even if it turned out - and it hasn't been shown yet, but even if did turn out that there were genes that distinguished between smokers who are more or less likely to develop lung cancer, it's very unlikely that those genes would also protect against the other adverse effects of cigarette smoking like heart diseaseā€¦

PALCA: Or any of the other cancers associated with smoking.

Dr. HUNTER: This is all about discovery and this is all about establishing specific genes that are associated with specific diseases. In this case, potentially a specific behavior.

PALCA: Hunter says genome-wide association studies have already turned up lots of new genes associated with diseases. And he says you can expect to hear about many more in the future.

Joe Palca, NPR News, Washington.

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