Protective cells could cut risk of lung cancer for ex-smokers

Quitting smoking could do more than just stop further damage to the lungs. It could also allow new, healthy cells to actively replenish the lining of our airways which could protect against cancer, according to UCL, UCLH and Wellcome Sanger Institute researchers funded by Cancer Research UK.

Researchers found that people who had stopped smoking had more genetically healthy lung cells, which have a lower risk of developing into cancer. They said the findings – published inNature – suggest it is never too late to quit smoking.

Lung cancer is the most common cause of cancer death in the UK, accounting for 21% of all cancer deaths. Smoking damages DNA and hugely increases the risk of lung cancer, causing around 72% of the 47,000 annual cases of lung cancer in the UK.

In the first major study of the genetic effects of smoking on ‘normal’, non-cancerous lung cells, researchers analysed lung biopsies from 16 people including smokers, ex-smokers, people who had never smoked and children.

Researchers looked at the pattern of genetic changes in these non-cancerous lung cells. They found that despite not being cancerous, more than 9 out of every 10 lung cells in current smokers had up to 10,000 extra genetic changes compared with non-smokers, and these mutations were caused directly by the chemicals in tobacco smoke. More than a quarter of these damaged cells had at least one cancer-driver mutation, which explains why the risk of lung cancer is so much higher in people who smoke.

Unexpectedly, in people who had stopped smoking, there was a sizable group of cells lining the airways that had escaped the genetic damage from past smoking. These cells looked like they came from people who had never smoked: they had much less genetic damage from smoking and would have a low risk of developing into cancer.

The researchers found that ex-smokers had four times more of these healthy cells than people who still smoked – representing up to 40% of the total lung cells in ex-smokers.

Professor Sam Janes, joint senior author from UCL and University College London Hospitals Trust, said: “Our study has an important public health message and shows that it really is worth quitting smoking to reduce the risk of lung cancer. Stopping smoking at any age does not just slow the accumulation of further damage, but could reawaken cells unharmed by past lifestyle choices. Further research into this process could help to understand how these cells protect against cancer, and could potentially lead to new avenues of research into anti-cancer therapeutics.”

While the study showed that healthy lung cells could start to repair the lining of the airways in ex-smokers and help protect them against lung cancer, researchers cautioned that smoking also causes damage deeper in the lung that can lead to emphysema – chronic lung disease. This damage is not reversible, even after stopping smoking.