Lung cancer is one of the most serious and deadly diseases in the world. Every year, millions of people are diagnosed, and many lose their lives to the illness.
While smoking is still the main cause of lung cancer, scientists have long known that air pollution also plays an important role.
Now, a large and detailed study has taken a closer look at how different types of air pollution are linked to different forms of lung cancer and how they may affect survival after diagnosis.
The study was led by researchers from the Barcelona Institute for Global Health and published in the journal Environmental Pollution. Instead of looking at lung cancer as one single disease, the researchers focused on its main subtypes. Lung cancer is usually divided into two broad groups. The most common group is non-small-cell lung cancer.
This group includes adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. These cancers develop in different types of lung cells and in different parts of the lung. Together, they account for most lung cancer cases. The second group is small-cell lung cancer. It is less common but more aggressive and is very strongly linked to smoking.
Outdoor air pollution has already been classified as a cause of lung cancer. Tiny particles in the air, known as fine particulate matter or PM2.5, are especially harmful because they can travel deep into the lungs when we breathe.
However, scientists still do not fully understand whether different air pollutants affect different lung cancer subtypes in different ways, or whether pollution influences how long people survive after they are diagnosed. This study was designed to answer those questions.
The researchers used data from a very large and long-running study in the United States called the Cancer Prevention Study-II. More than 122,000 adults took part. The study began in 1992, and participants were followed for up to 25 years, until 2017.
Every two years, they updated information about their health, lifestyle, and any cancer diagnoses. This long follow-up allowed researchers to observe how long-term exposure to air pollution affected lung cancer risk over decades.
To estimate air pollution exposure, the scientists used national air quality data combined with satellite images and information about land use. They calculated yearly exposure levels for several common air pollutants.
These included fine particles (PM2.5), larger particles (PM10), ozone, sulfur dioxide, nitrogen dioxide, and carbon monoxide. Importantly, the analysis also adjusted for many personal factors, especially smoking history, which is critical when studying lung cancer.
Over the 25-year period, 4,282 participants developed lung cancer. When the researchers analyzed the data, they confirmed that higher exposure to PM2.5 increased the risk of lung cancer.
This increased risk was seen across all major non-small-cell lung cancer subtypes, including adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. This finding strengthens earlier evidence that fine particle pollution is harmful to lung health no matter which type of lung cancer develops.
The study also uncovered important links between lung cancer and several gaseous air pollutants. Nitrogen dioxide, ozone, and sulfur dioxide showed clear associations with non-small-cell lung cancer. Nitrogen dioxide, which mainly comes from traffic and fuel combustion, was more strongly linked to adenocarcinoma, the most common lung cancer subtype.
Ozone was linked to a higher risk of large cell carcinoma. In contrast, these gaseous pollutants did not show consistent links with small-cell lung cancer, which suggests that smoking may play a much stronger role in that subtype than air pollution.
When the researchers looked at survival after lung cancer diagnosis, the results were more complex. Overall, air pollution did not show a clear effect on survival for all lung cancer patients combined.
However, among patients diagnosed at an early stage, higher exposure to sulfur dioxide was linked to lower survival. This suggests that pollution may still influence disease progression in certain groups, even after cancer is detected.
When reviewing these findings, several important points stand out. First, the study shows that air pollution does not affect all lung cancers in the same way. Different pollutants appear to be linked to different cancer subtypes, which helps explain why past research sometimes produced mixed results.
Second, the long follow-up period and large number of participants make the results more reliable than many earlier studies. Third, the findings highlight that environmental exposure should be considered alongside personal risk factors like smoking.
At the same time, the study also has limits. It cannot prove that air pollution directly causes specific lung cancer subtypes, and the survival findings apply only to certain patient groups. Still, the evidence strongly suggests that cleaner air could reduce lung cancer risk and possibly improve outcomes for some patients.
Overall, this research reinforces the idea that air quality is a major public health issue. Reducing pollution levels could help prevent lung cancer and protect vulnerable populations. It also suggests that doctors and health systems should consider environmental exposure when assessing cancer risk and planning patient care.
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The study is published in Environmental Pollution.
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