These people have genes that help limit mutations to DNA that would turn cells malignant and make them grow into tumors, the researchers say.
Scientists have long suspected that smoking leads to lung cancer by triggering DNA mutations in healthy cells. But it was hard for them to identify the mutations in healthy cells that might help predict future cancer risk, Jan Vijg, PhD, a senior author of the study and researcher at the University School of Medicine, Shanghai, China, said in a statement.
His team used a process called single-cell whole genome sequencing to examine cells lining the lungs of 19 smokers and 14 nonsmokers ranging in age from their pre-teens to their mid-80s. The cells came from patients who had tissue samples collected from their lungs during diagnostic testing unrelated to cancer. The scientists reported their findings in Nature Genetics.
The researchers specifically looked at cells lining the lungs because these cells can survive for years and build up mutations over time that are linked to aging and smoking.
“Of all the lung’s cell types, these are among the most likely to become cancerous,” says Simon Spivack, MD, a senior author of the study and professor at the Albert Einstein College of Medicine, New York.
Smokers had far more gene mutations that can cause lung cancer than nonsmokers, the analysis found.
“This experimentally confirms that smoking increases lung cancer risk by increasing the frequency of mutations, as previously hypothesized,” says Dr. Spivack. “This is likely one reason why so few nonsmokers get lung cancer, while 10 to 20 percent of lifelong smokers do.”
Among the smokers, people had smoked a maximum of 116 pack-years. A pack-year is the equivalent of smoking one pack a day for a year. The number of mutations detected in smokers’ lung cells increased in direct proportion to the number of pack-years they smoked.
But after 23 pack-years, the lung cells in smokers didn’t appear to add more mutations, the researchers report, suggesting that some people’s genes might make them more likely to fight mutations.
“The heaviest smokers did not have the highest mutation burden,” says Dr. Spivack. “Our data suggest that these individuals may have survived for so long in spite of their heavy smoking because they managed to suppress further mutation accumulation.”
While it’s possible these findings could one day help doctors come up with better ways to screen for lung cancer and treat the disease, that’s still a long way off. Many more lab tests and larger studies will be needed to better pinpoint which smokers might be more prone to lung cancer and why.
A version of this article first appeared on WebMD.com.