London: Researchers say they have cracked how air pollution leads to cancer, in a discovery that completely transforms our understanding of how tumours arise.
The team at the Francis Crick Institute in London showed that rather than causing damage, air pollution was waking up old damaged cells, BBC reported on Saturday.
One of the world's leading experts, Prof Charles Swanton, said the breakthrough marked a "new era". And it may now be possible to develop drugs that stop cancers forming.
The findings could explain how hundreds of cancer-causing substances act on the body.
The classical view of cancer starts with a healthy cell. It acquires more and more mutations in its genetic code, or DNA, until it reaches a tipping point. Then it becomes a cancer and grows uncontrollably, BBC said.
But there are problems with this idea: cancerous mutations are found in seemingly healthy tissue, and many substances known to cause cancer - including air pollution - don't seem to damage people's DNA.
The researchers have produced evidence of a different idea. The damage is already there in our cell's DNA, picked up as we grow and age, but something needs to pull the trigger that actually makes it cancerous, the BBC report added.
The discovery came from exploring why non-smokers get lung cancer. The overwhelming majority of lung cancers are caused by smoking but still, one in 10 cases in the UK is down to air pollution.
The Crick scientists focused on a form of pollution called particulate matter 2.5 (known as PM2.5), which is far smaller than the diameter of a human hair.
Through a series of detailed human and animal experiments they showed:
Places with higher levels of air pollution had more lung cancers not caused by smoking; breathing in PM2.5 leads to the release of a chemical alarm - interleukin-1-beta - in the lungs; this causes inflammation and activates cells in the lungs to help repair any damage; but around one in every 600,000 cells in the lungs of a 50-year-old already contains potentially cancerous mutations; and these are acquired as we age but appear completely healthy until they are activated by the chemical alarm and become cancerous.
Crucially, the researchers were able to stop cancers forming in mice exposed to air pollution by using a drug that blocks the alarm signal.
Dr Emilia Lim, one of the Crick researchers, said people who had never smoked but developed lung cancer often had no idea why.
"It's super-important - 99% of people in the world live in places where air pollution exceeds the WHO guidelines so it really impacts all of us."
The latest findings are being presented to scientists at a conference of the European Society for Medical Oncology. (UNI)