Lung cancer has long been seen as a disease mainly caused by smoking. However, doctors are now noticing a worrying pattern: more people who have never smoked are being diagnosed with lung cancer.
This increase is especially clear among women and in parts of East Asia, raising important questions about what else might be causing the disease.
A new international study has provided strong evidence that environmental factors may play a major role. The research, published in the journal Nature, suggests that air pollution and certain traditional herbal medicines could be important causes of lung cancer in people who have never smoked.
The study was led by scientists from the University of California San Diego and the U.S. National Cancer Institute. The team examined lung tumor samples from 871 people who had never smoked.
These individuals came from 28 regions around the world, including countries in Africa, Asia, Europe, and North America. The researchers chose participants from areas with different levels of air pollution so they could compare the effects.
To understand what might have caused the cancer, the scientists used a method called whole-genome sequencing. This technique allows researchers to study all of the DNA in a cell.
They looked for patterns known as mutational signatures, which are like fingerprints left behind by harmful exposures. These patterns can help identify what may have damaged the DNA and led to cancer.
The results showed a clear link between air pollution and DNA damage in lung tumors. People who lived in areas with higher pollution levels had more genetic mutations in their cancer cells.
Many of these mutations were known to drive cancer growth. Some of the patterns closely resembled those seen in people who smoke heavily, even though the individuals in this study had never smoked.
One particularly concerning finding was a large increase in a mutation pattern usually linked to tobacco exposure. In people exposed to higher pollution, this pattern appeared nearly four times more often. The researchers also found more mutations related to aging, suggesting that air pollution may speed up the aging process in lung cells.
The study found a clear dose-response relationship. This means that the higher the level of air pollution, the greater the number of mutations in the tumor. In addition, these tumors had shorter telomeres. Telomeres are protective parts at the ends of chromosomes, and shorter telomeres are a sign of cell damage and aging.
The researchers also looked at the effects of secondhand smoke. While exposure to secondhand smoke was linked to some signs of cell aging, it did not produce the same level of DNA mutations as air pollution.
This suggests that air pollution may have a stronger or more direct effect on genetic damage, although secondhand smoke is still known to be harmful.
Another important finding involved a substance called aristolochic acid. This chemical is found in some traditional herbal medicines and is already known to cause certain cancers.
In this study, its genetic signature was found in lung tumors, mainly in patients from Taiwan. The researchers believe that inhaling herbal products containing this substance could be one possible source, although more research is needed to confirm this.
The study also revealed something unexpected. The scientists found a new pattern of DNA changes that appeared in many lung cancers in non-smokers but not in smokers. The cause of this pattern is currently unknown.
It was not linked to air pollution, herbal medicines, or other known risks. This discovery suggests that there may be other hidden causes of lung cancer that scientists have not yet identified.
This research is part of a larger global effort to understand why lung cancer is increasing among non-smokers. The team plans to include more patients from regions such as Latin America, the Middle East, and other parts of Africa. They are also studying other possible risk factors, including exposure to radon, asbestos, marijuana smoke, and e-cigarettes.
The findings highlight the importance of looking beyond smoking when it comes to lung cancer. They also point to the need for better air quality and stronger regulation of harmful substances. Understanding how environmental factors affect our DNA could help prevent cancer in the future.
As one of the study leaders, Dr. Maria Teresa Landi from the National Cancer Institute, explained, this research is not only a scientific discovery but also an opportunity to improve public health by identifying risks early and reducing exposure.
The study provides new insight into the hidden causes of lung cancer and offers hope that, with more research, better prevention strategies can be developed.
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The findings were published in the journal Nature.
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