PARIS, Sept 10, 2022 (BSS/AFP) - Scientists said Saturday they had 
identified the mechanism through which air pollution triggers lung cancer in 
non-smokers, a discovery one expert hailed as "an important step for science 
-- and for society".

  The research illustrated the health risk posed by the tiny particles 
produced by burning fossil fuels, sparking fresh calls for more urgent action 
to combat climate change.

  It could also pave the way for a new field of cancer prevention, according 
to Charles Swanton of the UK's Francis Crick Institute.

  Swanton presented the research, which has not yet been published in a peer-
reviewed journal, at the European Society for Medical Oncology's annual 
conference in Paris.

  Air pollution has long been thought to be linked to a higher risk of lung 
cancer in people who have never smoked.

  "But we didn't really know whether pollution was directly causing lung 
cancer -- or how," Swanton told AFP.

  Traditionally it has been thought that exposure to carcinogens, such as 
those in cigarette smoke or pollution, causes DNA mutations that then become 
cancer. But there was an "inconvenient truth" with this model, Swanton said: 
previous research has shown that the DNA mutations can be present without 
causing cancer -- and that most environmental carcinogens do not cause the 
mutations.

  His study proposes a different model.

  - A future cancer pill? -

  The research team from the Francis Crick Institute and University College 
London analysed the health data of more than 460,000 people in England, South 
Korea and Taiwan.

  They found that exposure to tiny PM2.5 pollution particles -- which are 
less than 2.5 microns across -- led to an increased risk of mutations in the 
EGFR gene.

  In laboratory studies on mice, the team showed that the particles caused 
changes in the EGFR gene as well as in the KRAS gene, both of which have been 
linked to lung cancer.

  Finally, they analysed nearly 250 samples of human lung tissue never 
exposed to carcinogens from smoking or heavy pollution.

  Even though the lungs were healthy, they found DNA mutations in 18 percent 
of EGFR genes and 33 percent of KRAS genes.

  "They're just sitting there," Swanton said, adding that the mutations seem 
to increase with age.

  "On their own, they probably are insufficient to drive cancer," he said.

  But when a cell is exposed to pollution it can trigger a "wound-healing 
response" that causes inflammation, Swanton said. 

  And if that cell "harbours a mutation, it will then form a cancer", he 
added.

  "We've provided a biological mechanism behind what was previously an 
enigma," he said.

  In another experiment on mice, the researchers showed that an antibody 
could block the mediator -- called interleukin 1 beta -- which sparks the 
inflammation, stopping cancer from getting started in the first place.

  Swanton said he hoped the finding would "provide fruitful grounds for a 
future of what might be molecular cancer prevention, where we can offer 
people a pill, perhaps every day, to reduce the risk of cancer".

  - 'Revolutionary' -

  Suzette Delaloge, who heads the cancer prevention programme at France's 
Gustave Roussy institute, said the research was "quite revolutionary, because 
we had practically no prior demonstration of this alternative way of cancer 
forming.

  "The study is quite an important step for science -- and for society too, I 
hope," she told AFP.

  "This opens a huge door, both for knowledge but also for new ways to 
prevent" cancer from developing, said Delaloge, who was not involved in the 
research but discussed it at the conference on Saturday.

  "This level of demonstration must force authorities to act on an 
international scale."

  Tony Mok, an oncologist at the Chinese University of Hong Kong, called the 
research "exciting".

  "It means that we can ask whether, in the future, it will be possible to 
use lung scans to look for pre-cancerous lesions in the lungs and try to 
reverse them with medicines such as interleukin 1 beta inhibitors," he said.

  Swanton called air pollution a "hidden killer", pointing to research 
estimating it is linked to the deaths of more than eight million people a 
year -- around the same number as tobacco.

  Other research has linked PM2.5 to 250,000 deaths annually from lung cancer 
alone.

  "You and I have a choice about whether we smoke or not, but we do not have 
a choice about the air we breathe," said Swanton, who is also the chief 
clinician at Cancer Research UK, which was the main funder of the research.

  "Given that probably five times as many people are exposed to unhealthy 
levels of pollution than tobacco, you can see this is quite a major global 
problem," he added.

  "We can only tackle it if we recognise the really intimate links between 
climate health and human health."