Studies Link Genetic Variants to Lung Cancer

Smoking has long been recognized as the major cause of lung cancer. But now 3 separate research teams have identified variations in a genetic region that can also greatly raise the risk for developing this deadly disease. The findings may help to explain why some smokers develop lung cancer while others do not.

Smoking, the top cause of preventable death, prematurely kills about 5 million people worldwide each year. In the United States, nearly 90% of lung cancer deaths are caused by cigarette smoking. The connections between smoking and lung cancer are so strong that it can be difficult for genetic researchers to tease apart whether particular genes affect smoking behavior or lung cancer or both.

To look at this issue, 3 scientific groups, all funded in part by NIH, performed large, genome-wide scans of DNA samples from thousands of current and former smokers. Each searched for genetic variations linked to lung cancer, smoking behaviors and addiction. All 3 teams published their findings on April 3, 2008—2 in the journal Nature and the other in the online edition of Nature Genetics.

The 3 groups found that lung cancer risk was strongly tied to genetic variations in a tiny chromosome region that houses genes related to nicotine response. Recent studies already hinted that these genes—which encode subunits of nicotinic acetylcholine receptors—are linked to smoking behavior.

Although the 3 research teams pinpointed the same genomic regions as being involved in lung cancer, they reached different conclusions about their findings. Two of the groups—funded in part by NIH’s National Cancer Institute (NCI) and National Human Genome Research Institute (NHGRI)—concluded that the genetic variations boost lung cancer risk independent of how they may affect smoking behavior.

The third group—led by Dr. Kári Stefánsson of deCODE Genetics and funded in part by NIH’s National Institute on Drug Abuse (NIDA)—identified a genetic variant strongly linked to nicotine addiction and heavy smoking. They also found that the variant was associated with higher rates of both lung cancer and peripheral arterial disease. The scientists suggest that increased smoking is largely behind the elevated disease rates.

“The variant does not increase the likelihood that a person will start smoking,” Stefánsson explains, “but for people who do smoke it increases the likelihood of addiction.”

Further studies are needed to clarify how these genetic variants contribute to lung cancer. Larger studies will help determine whether the variants directly affect cancer risk or whether their major influence is via smoking behavior and its resulting impact on cancer.