Air Pollution As Lung Cancer Risk

It has been nearly 10 years since the World Health Organization listed air pollution as a risk factor for lung cancer. The International Agency for Research on Cancer (IARC; a part of the World Health Organization) Monograph Volume 109 has established a clear link between air pollution and lung cancer. It is estimated that air pollution contributes to 29% of lung cancer deaths worldwide.

Air pollution is a complex mixture of various pollutants originating from nature and human activities. Industrial processes, vehicular emissions and energy production release air pollutants like nitrogen dioxide, sulfur dioxide and other tiny particles, all recognized as carcinogens. Among these pollutants, fine particulate matter has the most profound impact on human health. 

A new study has shown that the tiny particles found in polluted air can trigger the development of lung cancer, but not by directly causing DNA mutations and alterations. Instead, it triggers a chain reaction of inflammatory responses that initiate tumor formation.

Researchers from The Francis Crick Institute presented the study outcome at the European Society for Medical Oncology (ESMO) Congress 2022 in Paris.

The researchers found that people regularly exposed to high levels of particulate matter with 2.5µm diameters (PM2.5) have a higher risk of EGFR mutant lung cancer, a lung cancer gene signature predominant to non-smokers.

“Cells with cancer-causing mutations accumulate naturally as we age, but they are normally inactive,” says Professor Charles Swanton, the lead scientist of this study.

EGFR mutation, often due to the normal aging process, exists even in healthy cells. Exposure to PM2.5 particles from air pollution triggers inflammation in the lungs. An inflammatory substance, interleukin 1β, transforms lung cells with pre-existing EGFR mutation into tumor cells.

The link between PM2.5 and lung cancer was tested in mice models and by epidemiological data from 400,000 people in England, Taiwan and South Korea. The results indicated a greater incidence of EGFR mutant lung cancer

PM2.5 particles are common pollutants from car exhaust, power generation, industrial activity and wood burning. You can find them at high levels in cities like many cities in Asia and South America and the cities suffering from wildfire.

In the US, over eight million people live in areas with unhealthy air quality due to wildfire smoke. These people are exposed to more than 100 micrograms (per cubic meter) of PM2.5 from wildfire smoke for at least one day per year.

Based on the WHO guidelines, the annual average concentration of PM2.5 an individual is exposed to should not exceed 5 micrograms per cubic meter.

A separate Canadian study found that people living within 50km (31 miles) of wildfires had a 5% higher risk of lung cancer than those living farther away. The study has followed two million Canadians for over 20 years to examine the association between wildfire and cancer risk.

Unlike pollutants released by automobiles or industry that the government can regulate, the wildfire is an “exceptional event” under the Clean Air Act – events that cannot be “reasonably controllable or preventable,”

It is essential for individuals residing in areas prone to wildfires to stay informed about air quality conditions, follow recommended guidelines for protecting their health, and consult healthcare professionals if needed.

Cancer was estimated to have claimed 2.8 million lives in China in 2015, with lung cancer being the most common and deadliest. There is a rising trend in lung cancer incidences among women and non-smokers and it “is not associated with tobacco use.”

A thoracic surgeon at Shanghai Pulmonary Hospital stressed the contribution of PM2.5, suspended in smog, as the main culprit of lung cancer, apart from smoking.

"The intense rise in lung cancer ... is intimately related to smog," says Dr. Zhao Xiaogang.

In 2017, Dr. Zhao’s poem, “I Long to Be King,” which ran in the CHEST Journal, went viral on Chinese social media. The poem personified lung cancer and abetted smog, “I've been nourished on the delicious mist and haze.” See here for the full poem.

I long to be king,

With my fellows swimming in every vessel.

My people crawl in your organs and body,

Holding the rights for life or death, I tremble with excitement.

A study by Hebei Medical University found that the number of lung cancer deaths attributed to PM2.5 in Hebei Province was almost a fifth of those attributed to smoking.

Hebei is known as the most polluted province in China. Along with Hebei, some other industrialized regions in northern China frequently battle against a hazardous concentration of PM2.5 – exceeding 300 micrograms per cubic meter.

While the situation may seem alarming, it is important to put the matter in perspective. The impact of PM2.5 is significantly lower compared to the risk associated with smoking. The recognition of PM2.5 as a lung cancer risk factor highlights its health implications, especially for non-smokers.