Clearing the Air: How Climate Change Is Affecting Lung Cancer

The first epidemiological studies linking lung cancer to smoking emerged in the 1950s, including work by British researchers Richard Doll and A. Bradford Hill, who postulated air pollution was a possible culprit for the rising rates of lung carcinoma.^1,2

“There were proposed links between air quality and lung cancer as far back as the 1950s and 1960s, resulting in things like the Clean Air Act, but we were still decades away from seeing the impact of air pollution, largely because of the confounder that is smoking,” said Panagis Galiatsatos, MD, MHS, an associate professor of medicine at Johns Hopkins Medicine.

The link between cigarette smoking and lung cancer risk was confirmed in the US Surgeon General’s 1964 report. Proving to be a call to action, the percentage of Americans who smoke is estimated to have decreased from more than 40% in 1964 to approximately 18% today.³

Researchers continued to explore other causes of lung cancer that were preventable, such as radon and secondhand smoke exposure. The American Cancer Society (ACS) did a large-scale study that linked air pollution to lung cancer and controlled for cigarette smoking. A separate study by the ACS focused on thousands of never-smokers and also linked long-term air pollution exposure to lung cancer mortality. The substantial body of evidence led the International Agency for Research on Cancer to classify indoor and outdoor air pollution as a Group 1 carcinogen, like smoking, in 2013.⁴

Climate Change and Air Quality

More than 70 years after the link between air pollution and lung cancer was proposed, a group of editors of health journals worldwide published an editorial in the New England Journal of Medicine with an urgent call to action to address climate change in order to “halt the destruction of nature and protect health.”⁵ In their editorial, the writers suggested that “better air quality alone would realize health benefits that easily offset the global costs of emissions reductions.”

One of the factors that affects air quality is indoor and outdoor air pollution. Air pollution affects and is affected by climate change, mostly through the burning of fossil fuels like coal, oil, and gas, which emit particulate matter when burnt. Even individuals who do not live in regions with poor air quality can be affected, as this particulate matter can be windblown as a result of drought or wildfire. Particulate matter in outside air can affect indoor air quality when it enters the home or the workplace through ventilation systems or windows.⁶ 

Defining the exact links between air quality and lung cancer is difficult. It is challenging to control for all factors, according to Daniel Boffa, MD, a professor of surgery at the Yale School of Medicine.

“It can be difficult to study pollution and lung cancer in the [United States] because there are a lot of microenvironments where people are exposed to different things,” Dr. Boffa said. “This can be affected by where people work, where they live, and where they travel to.”

Risk can be increased through a one-time high level of exposure, like the exposure many emergency workers experienced during the 9/11 clean-up effort, or through more long-term, low-level exposure.

Recently, though, more studies have begun to draw more scientific links between air quality, specifically particulate matter with an aerodynamic diameter less than 2.5 microns (PM_2.5), and lung disease.

Air Quality and Cancer Risk

In a recent review from the International Association for the Study of Lung Cancer Early Detection and Screening Committee, Christine D. Berg, MD, formerly of the National Cancer Institute and now retired, and colleagues estimated a nearly 30% increase in the number of attributable lung cancer deaths since 2007.⁷

“One climate change issue directly relevant to lung cancer is increases in wildfires,” Dr. Berg said.

A recent Canadian study looked for associations between long-term exposure to wildfires, which are known to emit carcinogenic pollutants, and incidence of specific cancers. Looking at more than 2 million individuals followed for a median of 20 years, the study showed that those exposed to wildfire within 50 km (about 30 miles) of their residence in the past 10 years had an approximately 5% increased incidence of lung cancer and a 10% greater risk of brain cancer compared with unexposed populations.⁸

Not long after the northeast United States was covered in smoke from wildfires in Canada in June, Drs. Zhang, Nogueira, and colleagues published a timely study discussing the association of wildfire exposure while recovering from lung cancer surgery with overall survival (OS). The team looked for associations between OS among more than 450,000 patients who underwent curative-intent surgery for non-small cell lung cancer (NSCLC) and active wildfire detected at the zip code of residence. Dr. Boffa, an investigator on the study, noted that exposure to wildfire was associated with worse OS after lung cancer surgery regardless of whether the exposure occurred 3, 4 to 6, or 7 to 12 months after surgery.⁹

“For patients who are already diagnosed, their lungs are already injured and incredibly fragile,” Dr. Galiatsatos said. “People going through treatment for lung cancer will be the most vulnerable population during moments of poor air quality. An analogy would be the recommendation for people with lung cancer to stop smoking … living in an area of poor air quality means being surrounded by the thing that may have caused the cancer to begin with.”

However, Dr. Galiatsatos said he doesn’t foresee occasional exposure to wildfire smoke alone being enough of a trigger to increase rates of lung cancer.

“If there is an increase it is more likely to be from a combination of man-made pollutants,” Dr. Galiatsatos said. “This will include proximity to factories and how many years someone is breathing that in or living in areas with high-density car travel.”

More evidence is pointing to a link between PM_2.5 air pollution and lung cancer risk. A study out of California found that increased exposure to certain air pollutants—NO₂, O₃, PM₁₀, and PM_2.5—had a negative effect on all-cause mortality among patients with localized disease.¹⁰

Researchers in China showed a relative increase in the risk for lung cancer associated with a 10 µg/m³ increase in 3-year PM_2.5. Conversely, a reduction in PM_2.5 exposure was associated with a decrease in incidence of lung cancer.¹¹

Last year, late-breaking data out of the European Society for Medical Oncology Congress 2022 detailed the possible mechanism linking particulate matter to risk for NSCLC. Looking at more than 400,000 individuals from England, South Korea, and Taiwan, increasing levels of PM_2.5 were associated with increased risk for EGFR-mutant NSCLC. The researchers found that particulate matter promoted “a macrophage response and a progenitor-like state in lung epithelium harboring mutant EGFR” and that it “increased tumor burden in three EGFR– or KRAS-driven lung cancer models.” In other words, cells that harbored these mutations could turn cancerous once exposed to these air pollutants.^12,13

Evidence demonstrating the link between poor air quality and lung cancer is mounting, but Dr. Berg said that air quality is not the only factor related to climate change that can affect lung cancer incidence or mortality.

“Other elements of climate change, other extreme weather events, can cause severe disruption in health care delivery,” Dr. Berg said. “Hurricane Harvey in Houston disrupted oncology care among patients getting radiation for lung cancer, and these patients experienced poorer survival because they could not access those facilities.”¹⁴

The effect of these storms can persist for months and years. Another study showed that individuals diagnosed with breast cancer who were exposed to Hurricane Katrina had worse long-term survival compared with those who were not exposed.¹⁵

What Can Be Done?

Clinicians with patients who are concerned about climate change or air quality can offer several pieces of advice, according to Dr. Boffa.

“People have to ask themselves what elements are within their control,” he said.

For example, for those dealing with exposure to wildfires or wildfire smoke, a lot of the dangerous components can be minimized by wearing an N95 mask on days with particularly high levels of pollutants and using high-efficiency particulate air filters or other high-grade filters in the home.

“There are heating and cooling filters that can catch a lot of these small particles,” Dr. Boffa said.

Dr. Berg said that people can also check air quality each day, similar to how one might check the temperature. The Environmental Protection Agency (EPA) offers a tool on its AirNow.gov website where one can enter their local city or zip code to get a current reading on air quality. Try to avoid spending time outside on days with poor-quality air, particularly any day with an Air Quality Index value higher than 100, according to the EPA.

“I also used another site called PurpleAir during the Canadian wildfire season,” Dr. Berg said. “The EPA has monitors located at certain fixed sites, but PurpleAir depends on citizen advocacy. You buy a monitor, put it in your backyard, and transmit data.”

It is important to think about indoor air quality as well, Dr. Berg noted. In addition to using air filters inside the home, it is important to assess a home for mold, which is increasing with climate change and increases in humidity and during flooding events.

Everyone acknowledged that change on a wider scale will be more difficult and that most, if not all, of the proposed “larger” solutions will be disruptive to the status quo.

For example, in response to the COVID-19 pandemic, the Centers for Disease Control and Prevention developed and launched the National Wastewater Surveillance System (NWSS) to track the presence of the SARS-CoV-2 virus in wastewater samples. The theory was that NWSS could provide an early warning that COVID-19 is spreading in a local community.¹⁶

“It took dysentery for us to update our own sewage system, realizing that even though it was probably one of the best in the world we could still make it better,” Dr. Galiatsatos said. “Air quality should be viewed in that same sense. Bad air quality looks no different to the eye than poor air quality. Monitoring air quality should be a priority, especially for preventing a cancer that is the leading cause of cancer morbidity and mortality in the [United States].”

Dr. Galiatsatos said that reducing factory and car emissions should also be national and global priorities.

Indeed, Dr. Berg said that phasing out the use of coal worldwide is one of the most important aspects of improving air quality.

“Bloomberg’s [Beyond Carbon initiative] has done a good job in helping to start to get coal plants shut down throughout the [United States], and it should be noted that I am not in favor of those plants being converted to natural gas plants because of the deleterious effect of methane,” Dr. Berg said. “I am a radiation oncologist, and I think nuclear power is a greenhouse-emission-free source of energy.”

Dr. Berg also mentioned regional partnerships like the Regional Greenhouse Gas Initiative, a cooperative, market-based effort among 12 states in the Northeast to cap and reduce CO₂ emissions from the power sector.

Unfortunately, in the United States, climate change remains a politically divided issue.¹⁷

“Banning cigarettes was a big partisan issue 30 or 40 years ago,” Dr. Galiatsatos. “At the end of the day, though, they can’t deny that lung cancer rates are going up worldwide, that it is happening more and more in nonsmoking patients, and that we have identified one factor that is influential. Regardless of politics, we all deserve to breathe fresh clean air.”

Leah Lawrence is a freelance health writer and editor based in Delaware.

References

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