Air Pollution: A Risk Factor For Lung Cancer?

Air pollution has been linked to lung cancer, with studies showing that particle pollution in the outdoor air we breathe—from sources such as vehicle exhaust, coal-fired power plants, and industrial sources—can cause lung cancer. In 2013, the World Health Organization (WHO) International Agency for Research on Cancer reviewed the available scientific evidence and concluded that particulate matter causes lung cancer. Research has also shown that exposure to particulate matter promotes the growth of cells in the lungs, which carry cancer-causing mutations, even in non-smokers. This has been supported by studies in mice, which suggest that tumour growth is triggered by inflammation caused by tiny particles, rather than genetic mutations.

Outdoor air pollution

PM2.5 refers to fine particles in the air with an aerodynamic diameter of less than 2.5 micrometers, which is around 3% of the width of a human hair. These particles are a result of environmental pollutants from transportation, power generation, vehicle exhaust, coal-fired power plants, and other industrial sources. Exposure to these particles has been linked to higher rates of lung cancer, with approximately 1 in 10 cases in the UK attributed to outdoor air pollution. Globally, around 300,000 lung cancer deaths in 2019 were associated with PM2.5 exposure.

Studies in mice have provided further evidence of the link between outdoor air pollution and lung cancer. These studies found that tumour growth was triggered by inflammation caused by tiny particles, rather than genetic mutations. When mice with EGFR mutations in their lungs were exposed to air pollution levels typically found in cities, cancers were more likely to develop compared to unexposed mice. This suggests that air pollution promotes the initiation of lung cancer in cells with driver gene mutations.

While smoking remains the biggest risk factor for lung cancer, outdoor air pollution is a significant contributor as well. The health risks associated with air pollution underscore the importance of reducing pollution levels to protect public health and lower the risk of lung cancer and other respiratory diseases.

Indoor air pollution

While outdoor air pollution is a major concern, indoor air pollution is also a critical issue, particularly in low and middle-income countries. Indoor air pollution is considered the seventh most important cause of lung cancer.

In a study conducted in Taiyuan, China, researchers found a strong association between lung cancer and multiple sources of indoor air pollution among non-smoking women. The odds of developing lung cancer were significantly higher for those with heavy exposure to secondhand smoke at work, a high frequency of cooking, and the use of solid fuels for cooking and heating.

Another study exposed mice with EGFR mutations in their lungs to air pollution levels typically found in cities. The results indicated that cancers were more likely to develop from cells carrying these mutations when exposed to air pollution.

Reducing indoor air pollution is crucial for lowering the risk of lung cancer. This can be achieved through interventions such as improved cooking stoves, better indoor ventilation, and the use of household filtration systems to reduce PM2.5 levels.

Particulate matter (PM2.5)

Particulate matter, or PM, is a mixture of many chemical species. It is a complex combination of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. Particles vary widely in size, shape, and chemical composition and may contain inorganic ions, metallic compounds, elemental carbon, organic compounds, and compounds from the Earth's crust.

Fine particulate matter, or PM2.5, is defined as particles that are 2.5 microns or less in diameter. These particles are so tiny that they can enter deep into the lungs. In 2013, the World Health Organization (WHO) International Agency for Research on Cancer reviewed the available science and concluded that particulate matter causes lung cancer. Research has found that exposure to PM2.5 in the air promotes the growth of cells in the lungs that carry cancer-causing mutations.

Globally, around 300,000 lung cancer deaths in 2019 were attributed to exposure to PM2.5. Long-term exposure to PM2.5 has been linked to premature death, particularly in people who have chronic heart or lung diseases, and reduced lung function growth in children. Children living in communities with high levels of PM2.5 have been found to have slower lung growth and smaller lungs at age 18 compared to children who lived in communities with low PM2.5 levels.

In a study of nearly half a million people living in England, South Korea, and Taiwan, exposure to increasing concentrations of PM2.5 was linked to an increased risk of non-small cell lung cancer (NSCLC) with EGFR mutations. The same study also found higher rates of other types of cancer in areas with high levels of PM2.5, including mesothelioma, anal, small intestine, and laryngeal carcinomas.

Inflammation caused by air pollution

Air pollution is a mix of tiny solid and liquid particles in the air. These particles can be made up of a number of components, such as acids, organic chemicals, metals, soil, and dust, as well as carbon monoxide, ozone, nitrogen dioxide, and sulphur dioxide.

Ozone, a powerful lung irritant, is a major cause of inflammation in the lungs. When inhaled, it reacts with the lining of the airways, causing inflammation and damage that can impact multiple body systems. Ozone exposure can also shorten lives. Even short-term exposure to ozone can cause breathing problems such as chest tightness, coughing, and shortness of breath. Long-term exposure can lead to lasting damage to respiratory health, including inflammation and systemic stress that can cause or worsen other diseases over time.

In addition to ozone, particulate matter (PM2.5) in the air has been linked to inflammation in the lungs, which can lead to cancer. PM2.5 is made up of tiny particles, around 3% of the width of a human hair, that can enter deep into the lungs and even enter the bloodstream, causing systemic damage to tissues and cells. Research has shown that exposure to PM2.5 promotes the growth of cells in the lungs that carry cancer-causing mutations. These mutations, in combination with inflammation, can trigger cells to grow uncontrollably, forming tumours.

The health impacts of air pollution depend on the types, sources, and concentrations of the pollutants, as well as the duration of exposure. Both short- and long-term exposure to air pollution can have negative health consequences. While air pollution levels in the United States have been decreasing, it is clear that more work needs to be done to reduce harmful particle pollution.

Lung cancer mortality rates

Lung cancer is the leading cause of cancer death overall and among both men and women. In 2021, 134,592 people died from lung cancer, or 22% of all cancer deaths. Of these deaths, 71,549 were men and 62,955 were women. The lung cancer death rate in 2021 was 37% higher among men (37.4 per 100,000 population) than women (27.3 per 100,000). Death rates have been decreasing over the last decade, with rates decreasing by 35% for men and 26% for women in the last 10 years, and 20% for men and 14% for women in the last 5 years.

In the United States in 2021, 209,500 new lung cancers were reported and in 2022, 131,888 people died from lung cancer. Lung cancer screening is recommended for people who are at high risk due to their smoking history and age. Among people diagnosed with lung cancer from 2016 to 2020, 438,655 were still alive on January 1, 2021.

The COVID-19 pandemic disrupted health services, leading to delays and reductions in cancer screening and diagnosis, which may have contributed to lower incidence for most cancer sites in 2020. The numbers of new cases diagnosed in 2021 were a little lower than expected for some cancer types but returned to pre-pandemic counts for other cancer types.

While smoking remains the biggest risk factor for lung cancer, outdoor air pollution causes roughly 1 in 10 cases of lung cancer in the UK. Globally, around 300,000 lung cancer deaths in 2019 were attributed to exposure to PM2.5, fine particles that can enter deep into the lungs and are linked to lung cancer. Research has shown that exposure to PM2.5 promotes the growth of cells in the lungs that carry cancer-causing mutations.

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