Smokers who have been given a clean bill of health from their doctors after normal examination results may still have early signs of lung cancer, according to a study published in the journal Stem Cells.
Researchers at Weill Cornell Medical College, New York, compared a group of 21 healthy smokers with 31 smokers who had no detectable form of lung disease after X-rays and standard chest examinations.
The researchers sent a bronchoscope and a fine brush into the lungs of both groups to collect cells from the airway linings. The cells being examined formed a part of the airway epithelium, which comes into contact with cigarette smoke and is where lung cancer begins, the researchers say.
Results revealed that in the lining of the airways in the smokers' lungs, human embryonic stem cell genes had been activated, which are switched on in the most aggressive, hard-to-treat lung cancers, the researchers say.
Dr Robert Crystal, chairman and professor of genetic medicine at Weill Cornell Medical College, told Medical News Today:
"Cells that are lining the airways in smokers are in a more primitive state and have some of the features that you see in lung cancers.
So, basically, the guy smoking outside the building who thinks he is normal is already on his way to developing lung cancer."
The researchers say that the primitive cells they found do not normally appear in the healthy lung. They explain that healthy lung cells have very specific assignments. Healthy lung cells only express genes related to lung function, just as brain cells, for example, only express brain-specific genes.
The scientists explain that the loss of control seen in cancer cells means they can "multiply without restraint", enabling them to migrate to other organs. The study revealed that smokers' cells in their airway linings had already started losing this control.
Dr. Crystal says that although the researchers cannot say exactly how many cigarettes will cause early cell damage within the lungs and over what period, it is not only smokers who are at risk. Dr. Crystal says:
"What we do know is that in occasional smokers and passive smokers, they already have biological changes in their airways. With any smoke you are exposed to, your airways cells are being programed in an abnormal fashion."
The US National Cancer Institute says that quitting smoking is always worthwhile and that lung cancer is not inevitable. The institute says, for example: "Studies have shown that smokers who quit at about age 30 reduce their chance of dying prematurely from smoking-related diseases by more than 90%."
The researchers add that although many smokers undergo routine check-ups, physical examinations, X-rays and lung function tests, these are not sensitive enough to pick up the early cell changes in the lungs, which is misleading for the patient.
Dr. Crystal would like the research in his field to contribute to the development of treatments that target the early changes caused by smoking. He says:
"If we can target the cell changes and invent drugs that can reverse this, that is one important process. If we could have drugs that help protect the lung, that would solve a lot of problems.
"We know that smoking is bad. We know that 20% of smokers develop either emphysema or lung cancer. What we also know is that there are a lot of smokers who don't get that disease, and if we can understand the biology of the difference between those who develop lung disease and those who don't, that would also give us targets to develop new therapies."