- James Gallagher
- BBC science and medical correspondent
10 September 2022, 09:57 GMT
Researchers announce that they have discovered how air pollution leads to cancer, in a discovery that completely changes our understanding of how tumors develop.
The research team at the Francis Crick Institute in London showed that instead of causing damage, air pollution wakes up old damaged cells.
Professor Charles Swanton, one of the world’s leading experts, said the hack represented a “new era”.
It may now be possible to develop drugs that stop the formation of cancers.
The results might explain how hundreds of carcinogens act on the body.
The classic view of cancer begins with a healthy cell. They acquire more and more mutations in their genetic code, or DNA, until they reach a tipping point. Then it becomes a cancer and grows uncontrollably.
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 – do not appear to damage people’s DNA.
What is happening?
The researchers provided evidence for a different idea. The damage is already in the cells’ DNA, and it reactivates as we age, but something needs to pull the trigger that actually makes it cancerous.
The discovery came from research into the cause of lung cancer in non-smokers. The vast majority of lung cancers are caused by smoking, but one in 10 cases in Britain is still due to air pollution.
The Crick Institute scientists focused on a form of pollution called particulate matter 2.5 (PM2.5), which is much smaller than the diameter of a human hair.
Through a series of detailed human and animal experiments, they demonstrated:
- Places with higher levels of air pollution had more non-smoking lung cancers.
- With breathing, inhalation of PM2.5 triggers a chemical alarm – interleukin-1-beta – in the lungs.
- This causes inflammation and activates cells in the lungs, to help repair any damage.
- But regarding 1 in 600,000 cells in the lungs of a 50-year-old actually contain potentially cancerous mutations.
- This cell is acquired as we age, but appears to be completely healthy until it is activated by a chemical alarm and becomes cancerous.
Crucially, the researchers were able to prevent the formation of cancers in mice exposed to air pollution, by using a drug that blocks the alarm signal.
The results are impressive for understanding the impact of air pollution as well as the basics of how cancer develops.
Dr. Emilia Lim, one of the Crick Institute researchers, says that people who have never smoked but developed lung cancer often have no idea why.
“Giving them some clues regarding how this happened is really important,” she said.
“It’s critical. 99 percent of the people in the world live in places where air pollution exceeds WHO guidelines, so it really affects all of us.”
photo released, Getty Images
The findings might lead to a rethinking of how cancers form
Rethinking Cancer
But the results also showed that mutations alone are not always enough to cause cancer. And you may need an additional component.
Professor Swanton said this was the most exciting discovery his lab had come across, because it “actually rethinks our understanding of how tumors arise”. He said it would usher in a “new era” for molecular cancer prevention.
The idea of taking a cancer pill, if you live in a highly polluted area, is not entirely fanciful. Doctors have already tried interleukin-1-beta in cardiovascular disease and found, purely by chance, that it reduces the risk of lung cancer.
Meanwhile, these findings are being presented to scientists at a conference of the European Society of Medical Oncology.
Speaking to the BBC from the conference, Professor Swanton said: “Pollution is a great example, but there will be 200 more examples of that in the next 10 years.”
He said we need to rethink how smoking causes cancer – is it just the known DNA damage caused by the chemicals in tobacco, or does smoke cause inflammation as well?
Oddly enough, the idea that mutated DNA is not enough to form cancer, and that cancers need another growth stimulus, was first proposed by Isaac Brinblum in 1947.
“Philosophically speaking, it’s pretty cool,” says Dr. Lim. “Incredible biologists have done this work for 75 years, and it’s been largely ignored.”
However, Michelle Mitchell, chief executive of Cancer Research UK, stressed that “smoking is still the biggest cause of lung cancer”.
But she added: “The science, which takes years of hard work, is changing our thinking regarding how cancer develops. We now have a better understanding of the driving forces behind lung cancer.”