Smokers who appear to have evaded lung problems actually harbor cells that show early signs of impairment similar to those found in lung cancer, researchers have discovered.

Activation of the human embryonic stem cell (hESC)–signature genes has been observed in various epithelial cancers, explained a team led by Ronald G. Crystal, MD, chairman and professor of genetic medicine at Weill Cornell Medical College, New York, New York, in a Stem Cells paper. These genes are normally expressed in developing embryos but are also activated in the most aggressive lung cancers.

In their own study of 21 healthy nonsmokers and 31 smokers with no symptoms of lung disease and normal x-ray and chest findings,  Crystal and colleagues used a bronchoscope to collect cells from each participant’s airway epithelium. The investigators found that the hESC signature is selectively induced in the airway basal stem/progenitor cell population of healthy smokers, with a pattern similar to that activated in all major types of human lung cancer.

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“We were surprised to see that the smokers were expressing these very primitive human embryonic stem cell genes,” Crystal affirmed in a statement from Weill Cornell Medical College. “These genes are not normally functioning in the healthy lung.”

As Crystal noted, smoking strips lung cells of some of their genetic programming, and they take on the appearance of more primitive cells. “It doesn’t necessarily mean you will develop cancer, but the soil is fertile to develop cancer.”

Because physical examinations, lung function tests, and chest x-rays are not sensitive enough to pick up these very early changes, smokers with no remarkable findings on routine checkups may believe that their lungs have incurred no smoking-related damage.