- James Gallagher
- BBC science and medical correspondent
Researchers announce that they have discovered how air pollution leads to cancer, 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 is now possible to develop drugs that stop the formation of cancer.
The results could explain how hundreds of carcinogens act on the body.
The classic view of cancer starts 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: Cancer mutations are found in apparently healthy tissue, and many substances known to cause cancer — including air pollution — don’t seem to damage people’s DNA.
What is happening?
The researchers provided evidence for a different idea. The damage is already in the DNA of the cells and is reactivated as we age, but something has to pull the trigger that 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 ten cases in Britain is still due to air pollution.
The scientists at the Crick Institute 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 showed:
- Places with more air pollution had more nonsmoking lung cancers.
- When inhaled, inhalation of PM2.5 causes a chemical alarm – interleukin-1 beta – in the lungs.
- This causes inflammation and activates cells in the lungs to help repair any damage.
- But about 1 in 600,000 cells in the lungs of a 50-year-old may contain cancer-causing mutations.
- This cell is acquired as we age, but appears to be completely healthy until triggered by a chemical alarm and becomes cancerous.
Crucially, the researchers were able to prevent cancer from forming 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 and the basics of how cancer develops.
dr. Emilia Lim, one of the researchers at the Crick Institute, says that people who have never smoked but have developed lung cancer often have no idea why.
“Giving them some clues as to how this happened is very important,” she said.
“It’s critical. 99 percent of the world’s people live in places where air pollution exceeds WHO guidelines, so it affects us all.”
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, as it “actually rethinks our understanding of how tumors form”. 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 fantasy. 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.
Professor Swanton told the BBC from the conference: “Pollution is a great example, but there will be 200 more 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 too?
Curiously, the idea that mutated DNA is not enough to form cancer, and that cancers require a different growth stimulus, was first proposed by Isaac Brinblum in 1947.
“Philosophically, it’s pretty cool,” says Dr. Lim. “Incredible biologists have been doing this work for 75 years and it has been largely ignored.”
However, Michelle Mitchell, chief executive of Cancer Research UK, emphasized that “smoking is still the number one cause of lung cancer”.
But she added: “The science, which takes years of hard work, is changing our thinking about how cancer develops. We now have a better understanding of the drivers behind lung cancer.”