China’s soupy winter smogs used to make global headlines, and despite a fall in air pollution exposure in recent years, they may have done invisible damage that is only now coming to light.
China tops the world when it comes to cases of lung adenocarcinoma, a form of cancer that is becoming more prevalent, possibly due to particulate air pollution, according to a recent report from a body linked to the World Health Organization.
Lung adenocarcinoma has emerged as the predominant form of lung cancer around the world in recent years, with increasing risks observed among younger generations, particularly females, in most countries, according to a recent study by the International Agency for Research on Cancer.
Published in The Lancet Respiratory Medicine, the study “highlights that the largest burden of lung adenocarcinoma attributable to ambient particulate matter pollution was estimated in East Asia, particularly China,” the agency said in a statement marking World Cancer Day.
In 2022, more than 68% of global adenocarcinoma cases in men were in China, while Chinese women accounted for more than 70% of global cases in women.
The study authors think there could be a strong link to particulate air pollution.
“We examine changes in risk in different countries across successive generations and assess the potential burden of lung adenocarcinoma linked to ambient PM pollution,” study lead author Freddie Bray said.
“The results provide important insights as to how both the disease and the underlying risk factors are evolving, offering clues as to how we can optimally prevent lung cancer worldwide.”
Shift to another form of cancer
The study analyzed global, population-based cancer data for 2022, and found that adenocarcinoma was now the predominant form of lung cancer, a shift away from squamous cell carcinoma.
It said the shift was likely linked to changes in smoking patterns and exposure to environmental pollutants, estimating that 114,486 cases in men and 80,378 in women were related to air pollution, with East Asia, especially China, being the most affected region.
Global ambient fine particulate matter (PM2.5) air pollution is responsible for millions of annual premature deaths and trillions of US dollars of social costs.
There has been a marked post-2011 decrease in particulate pollution, largely driven by decreasing PM2.5 exposure in China, Nature Communications reported in 2023, adding that India has become the leading contributor to global ambient PM2.5 exposure since 2015.
But some 99% of the global population lives in an area where air quality doesn’t meet international standards for good health, currently set at 5 micrograms per cubic meter for the smallest and most lethal particle, PM2.5.
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In 2017, more than 30% of Chinese households still used solid fuels for heating and cooking, suggesting that indoor air pollution could also be a driving factor behind this type of cancer.
Charles Swanton, clinical professor at the Francis Crick Institute, a British biomedical research institute, discovered in 2022 that EGFR genetic mutations cause lung cancer in non-smokers.
He told RFA Mandarin in a recent interview that the EGFR mutation is a common driver mutation associated with lung adenocarcinoma.
“We don’t know why EGFR mutant lung cancer is so prevalent in Asia,” Swanton said. “One of the theories that we have is that air pollution is a contributor to the prevalence of these mutations.”
“Data from our lab shows that, in normal tissue that’s been exposed to air pollution, it’s easier to identify EGFR mutant clones- suggesting that these clones expand preferentially in lung damaged by particulate matter,” he said.
“In other words, the air pollution creates a fertile soil upon which the seed, which is the EGFR mutation, can grow.”
But he said the biggest risk factor for lung cancer is still smoking.
“[Smoking] puts you at about a 30-fold increased risk of lung cancer,” he said. “The risk of air pollution... is a lot less, probably less than threefold, (or at least 10 times lower than tobacco exposure) depending on the area you live in on the planet.”
“The reason why it’s such a problem is that so many more people are exposed to air pollution than they are to tobacco smoke,” Swanton said.
Cases of never-smokers
As smoking rates decline in many countries around the world, the proportion of lung cancer cases in people who have never smoked has increased, making it the fifth most common cancer to cause death.
Almost all cases in never-smokers are lung adenocarcinoma, which is also the most common form of lung cancer in women and residents of East Asia.
While CAT scans have boosted survival rates with better imaging allowing cancers to be detected sooner, Swanton said his lab is also working on ways to screen non-smoking populations for lung cancer, and that concrete progress could be seen in as little as 18 to 20 months.
The number of smokers in China has fallen significantly since the 1990s, but lung cancer edged out liver cancer as the top cancer killer in China in 2012.
Smoking rates among Chinese adults fell from 28.1% in 2010 to 24.1% in 2022. In 2019, the smoking rate among Chinese men aged 15 and over was 49.7%, a fall of 18.2% from 1990, while the smoking rate among women was 3.5%, down 20.9% from 1990.
A 2022 report from China’s National Cancer Center showed that of the 2.5742 million people who died of cancer that year, 733,300 died from lung cancer and 316,500 from liver cancer.
Norman Edelman, Professor of Preventive Medicine, Internal Medicine, and Physiology and Biophysics at the State University of New York, said the change in lung cancer types was “a kind of conundrum.”
“The evidence is pretty strong that particulate air pollution is a risk factor for lung cancer,” he said. “And it is true we’re beginning to see more women, especially young women, have lung cancer even though they haven’t smoked.”
“The prevailing hypothesis about the cause of many cancers is the so-called inflammation hypothesis, so things that get into the lung and cause inflammation and cause outpouring of all kinds of chemicals and response to the inflammation... which applies to both cigarette smoke and air pollution,” Edelman said.
Translated by Luisetta Mudie.