Protective cells could cut risk of lung cancer for ex-smokers.
Cancer Research UK-funded researchers have determined that it could be never too late to quit smoking.
Scientists from the Wellcome Sanger Institute and UCL have discovered that compared to current smokers, people who had stopped smoking had more genetically healthy lung cells, which have a much lower risk of developing into cancer.
The research shows that quitting smoking could do much more than just stopping further damage to the lungs. Researchers believe it could also allow new, healthy cells to actively replenish the lining of our airways. This shift in proportion of healthy to damaged cells could help protect against cancer.
These results highlight the benefits of stopping smoking completely, at any age.
Lung cancer is the most common cause of cancer death in the UK, accounting for 21% of all cancer deaths*. Smoking tobacco damages DNA and hugely increases the risk of lung cancer, with around 72 per cent of the 47,000 annual lung cancer cases in the UK caused by smoking**.
Damage to the DNA in cells lining the lungs creates genetic errors, and some of these are ‘driver mutations’, which are changes that give the cell a growth advantage. Eventually, an accumulation of these driver mutations can let the cells divide uncontrollably and become cancerous. However, when someone stops smoking, they avoid most of the subsequent risk of lung cancer***.
The researchers 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 – mutations – 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.
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.
Joint senior author Dr Peter Campbell, from the Wellcome Sanger Institute, said: “People who have smoked heavily for 30, 40 or more years often say to me that it’s too late to stop smoking – the damage is already done. What is so exciting about our study is that it shows that it’s never too late to quit – some of the people in our study had smoked more than 15,000 packs of cigarettes over their life, but within a few years of quitting many of the cells lining their airways showed no evidence of damage from tobacco.”
* Data were provided by: the Office for National Statistics on request, November 2018; ISD Scotland on request, October 2018; the Northern Ireland Cancer Registry on request, March 2019.
** Calculated by the Statistical Information Team at Cancer Research UK, 2018. Based on Brown KF, Rumgay H, Dunlop C, et al. The fraction of cancer attributable to known risk factors in England, Wales, Scotland, Northern Ireland, and the UK overall in 2015. British Journal of Cancer 2018; and incidence data were provided by the National Cancer Registration and Analysis Service (part of Public Health England), on request through the Office for Data Release, August 2018; ISD Scotland on request, April 2018; the Welsh Cancer Intelligence and Surveillance Unit, Health Intelligence Division, Public Health Wales on request, February 2019; the Northern Ireland Cancer Registry on request, April 2018.
*** Lung cancer risk, particularly squamous cell carcinoma risk, is much lower in people who used to smoke compared with people who currently smoke, and the gap widens as time since quitting smoking increases. Lung cancer risk in people who used to smoke who quit around 7 years previously is 43 per cent lower compared with current smokers. Lung cancer risk in ex-smokers who quit around 12 years previously is 72 per cent lower compared with people who currently smoke.
Lee PN, Forey BA, Coombs KJ. Systematic review with meta-analysis of the epidemiological evidence in the 1900s relating smoking to lung cancer. BMC Cancer. 2012 Sep 3;12:385.
**** Patients donated tissue from bronchoscopy investigations for other issues. The bronchial epithelium tissue used in this study was normal rather than diseased tissue.
Kenichi Yoshida and Kate Gowers et al. (2019). Tobacco exposure and somatic mutations in normal human bronchial epithelium. Nature. DOI: 10.1038/s41586-020-1961-1
You can read the Cancer Research UK press release in full here.