“The highest burden is estimated in East Asia, especially in China,” says Luo.

Air pollution levels in Europe and the US have fallen in recent decades. But the effect of changes on lung cancer rates has not yet become apparent. “It probably takes 15 to 20 years for changes in exposure to be reflected in lung cancer rates, but we don’t know for sure,” says Christine Berg, a retired oncologist from the National Cancer Institute in Maryland, US. Moreover, the picture is not static: climate change is likely to have an impact in the future. “With the increasing risk of wildfires, air pollution and PM2.5 levels are rising again in certain regions of the US,” says Berg. “At least one study has shown an association between wildfire exposure and increased incidence of lung cancer. Transitioning away from coal, oil and gas is therefore crucial not only to slow global warming but also to improve air quality.”

In 2021, the WHO halved the annual mean air quality guideline for PM2.5, meaning it has adopted a more stringent approach to particulate matter. “But 99% of the world population lives in areas where air pollution levels exceed [these updated] WHO guideline limits,” says Ganfeng Luo, a postdoctoral researcher at the International Agency for Research on Cancer (IARC) in Lyon, France.

In a recent study, IARC researchers estimated that approximately 194,000 cases of lung adenocarcinoma worldwide were attributable to PM2.5 in 2022. “The highest burden is estimated in East Asia, especially in China,” says Luo.

In the future, the number of lung cancer deaths attributable to air pollution could increase in countries such as India, which currently has some of the highest levels of air pollution, according to the WHO. In Delhi, the average PM2.5 levels are above 100 micrograms per sq m, which is 20 times above the WHO air quality guidelines.

In the UK, 1,100 people developed adenocarcinoma of the lung as a result of air pollution in 2022, the IARC study found. “But not all of these cases will be in never-smokers,” says Harriet Rumgay, an epidemiologist and a co-author of the study. Adenocarcinoma also occurs in smokers, especially in those using filtered cigarettes. “There’s still a lot we don’t know,” says Rumgay. “More research is needed to disentangle the different factors and also to understand, for example, how long you would need to be exposed to air pollution before developing lung cancer.”

As treatments continue to improve, lung cancer in never-smokers is becoming more survivable. It is conceivable that this type of lung cancer will one day become the most common form of a disease that has historically been associated with older male smokers, changing the way we think about the disease in popular culture; “…the idea that they [patients] are at least partly to blame for their disease is unfortunately still widespread,” says Wicki.

Martha was found to have an EGFR mutation and has been taking an inhibitor since her diagnosis almost three years ago. “It’s definitely not a vitamin pill,” she says. The drug has some nasty side effects: chronic fatigue, muscle pain, skin problems. Balancing the risks and benefits of drug treatment and maintaining a reasonable quality of life is not always easy, she says. But the drug is working.  “And the fatalistic view of the disease is changing, and that is good.”