While lung cancer continues to be the deadliest form of cancer globally, people who have never smoked are making up a growing proportion of those who are battling the disease. In 2022, about 2.5 million people were diagnosed with it.
Fewer smokers in many countries — including the U.S. — may account for some of that shift in cancer causation. But air pollution may also be playing a growing role, according to a World Health Organization study published in the Lancet Respiratory Medicine journal.
The study estimates that lung cancer in people who have never smoked cigarettes or tobacco in any form is now the fifth highest cause of cancer deaths worldwide. The forms of lung cancer are also shifting along with the causes.
Lung Cancer Causation
Lung cancer in people who’ve never smoked is almost exclusively adenocarcinoma. That form of cancer is now the most prevalent of the four main subtypes for both men and women globally. The other subtypes are squamous cell carcinoma, small-cell carcinoma, and large-cell carcinoma.
About 200,000 cases of adenocarcinoma were associated with exposure to air pollution in 2022, with the largest load in east Asia — particularly China, according to the study. Adenocarcinoma accounted for 45.6 percent of global lung cancer cases among men and 59.7 percent of global lung cancer cases among women in 2022. In 2020, the respective figures were 39.0 percent among men and 57.1 percent among women.
Read More: Developing A Drug To Identify And Target Tricky Cancer Cells
Shifting Demographics
There are also some demographic shifts in lung cancer — particularly by gender. While men continue to account for most lung cancer cases, with about 1.6 million globally in 2022, the gender gap is narrowing. About 900,000 women were diagnosed with the disease in 2022.
That shift has been underway for a while. An earlier study showed that during 1991 to 2018, the proportion of never smokers increased among both men (35.1 percent to 54.6 percent) and women (54.0 percent to 65.4 percent). Compared with current or former smokers, those who had never smoked had an 86 percent lower incidence of lung cancer death.
Cancer experts say smoking rates peaked much earlier in men than women. Women should now monitor for lung cancer as vigilantly as they do for breast cancer, the study notes.
Seeking Causal Connections
Many unknowns remain. Although the data now shows a correlation between air pollution and lung cancer, researchers have not yet firmly established a causal link. Scientists will likely increase investigating that potential connection, as well as search for other possible causes of lung cancer besides smoking and air pollution.
“Air pollution can be considered an important factor that partly explains the emerging predominance of adenocarcinoma that accounts for 53 percent to 70 percent of cases of lung cancer among people who have never smoked worldwide,” according to the study.
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Lancet Respiratory Medicine. Estimated worldwide variation and trends in incidence of lung cancer by histological subtype in 2022 and over time: a population-based study
Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
