The proportion of lung cancer cases among people who have never smoked is rising globally, with air pollution emerging as a significant contributor, according to a new study by the International Agency for Research on Cancer (IARC), the World Health Organization's (WHO) cancer research arm.
Lung cancer in never-smokers is now the fifth leading cause of cancer deaths worldwide, with adenocarcinoma-a subtype of lung cancer-accounting for the majority of cases in this population. In 2022 alone, an estimated 200,000 cases of adenocarcinoma were linked to air pollution, the study, published in The Lancet Respiratory Medicine, reported.
Lung cancer remains the leading cause of cancer-related deaths globally, with 2.5 million new cases diagnosed in 2022. Historically, smoking has been the primary driver of lung cancer, but shifting smoking patterns and increased exposure to environmental pollutants have altered the disease's landscape.
Dr. Freddie Bray, head of the IARC's cancer surveillance branch, emphasized the evolving nature of lung cancer risks. "With declines in smoking prevalence-as seen in the UK and US-the proportion of lung cancers diagnosed among those who have never smoked tends to increase," he stated.
According to IARC data, adenocarcinoma accounted for 45.6% of lung cancer cases in men and 59.7% in women in 2022, a notable rise from 39% and 57.1% in 2020, respectively. Among non-smokers, adenocarcinoma makes up between 53% and 70% of cases.
As smoking rates decline in many parts of the world, air pollution has emerged as a leading environmental factor contributing to lung cancer risk. The study identified East Asia-particularly China-as the region bearing the highest burden of adenocarcinoma cases attributed to air pollution.
"Air pollution can be considered an important factor that partly explains the emerging predominance of adenocarcinoma," the study reported.
The WHO estimates that nearly the entire global population lives in areas with air quality levels below WHO-recommended safety standards. Pollutants such as fine particulate matter (PM2.5), nitrogen oxides, and industrial emissions are known carcinogens that increase lung cancer risk even in non-smokers.
While lung cancer incidence among men has generally declined over the past four decades, cases among women continue to increase, further narrowing the gender gap. In 2022, 1.6 million men and 900,000 women were diagnosed with lung cancer, with current trends suggesting continued growth in female cases.
Recent studies in the UK and US have highlighted a growing number of lung cancer cases in women surpassing those in men, a shift largely attributed to historical smoking patterns and environmental factors.
Cancer experts warn that women should be as vigilant about lung cancer symptoms as they are about breast cancer.
The study's findings underscore the need for urgent cancer prevention strategies that target both tobacco control and air pollution reduction. Dr. Bray highlighted that understanding evolving risk factors will be crucial for developing effective public health policies.
"The diverging trends by sex in recent generations offer insights to cancer prevention specialists and policymakers seeking to develop and implement tobacco and air pollution control strategies tailored to high-risk populations," Bray said.