With approximately 2.5 million people diagnosed in 2022, lung cancer remains the most common cancer in the world. While the majority of cases are still diagnosed in men (1.6 million), the gap with women tends to narrow (910,000 cases), notes this study published in the journal Lancet Respiratory Medicine on the occasion of World Cancer Day.
Of the four major subtypes of lung cancer, adenocarcinoma has become predominant in women in 185 countries worldwide and in men in 150 countries (excluding those in Eastern Europe and Western Asia), according to the analysis of data from the World Health Organization's cancer agency, IARC.
“The fifth leading cause of cancer-related death worldwide”
In 2022, it represented nearly one in two cases of lung cancer in men (45.6%, or 717,211 cases), and six in ten (59.7%, or 541,971 cases) in women, compared to 39% and 57.1% respectively estimated in 2020. It is thus far ahead of the three other types: squamous cell carcinoma (29.4%), small cell carcinoma (11.5%), closely linked to tobacco consumption, and large cell carcinoma (6.5%), which is rarer.
Changes in cigarette manufacturing and smoking practices since the 1950s may have played a role in this shift. But smoking prevalence continues to decline in many countries, while the proportion of lung cancers among nonsmokers has increased, the researchers note.
Lung cancer in non-smokers has even become "the fifth leading cause of cancer-related death worldwide, occurring almost exclusively as adenocarcinoma and most commonly in women and Asian populations," the study highlights.
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"53 to 70% of lung cancer cases in non-smokers worldwide"
After a series of analyses, she concluded that "Air pollution can be considered as an important factor that partially explains the increasing prevalence of adenocarcinoma – which accounts for 53 to 70% of lung cancer cases in non-smokers worldwide."
Among the adenocarcinomas diagnosed in 2022, nearly 200,000 were thus associated with ambient air pollution by fine particles: 114,486 cases in men and 80,378 cases in women, according to their estimate. Since 2019, approximately 99% of the world's population lives in areas that do not meet WHO air quality criteria, according to the organization's figures.
In "In some countries with rapidly transitioning economies such as China, where a steady increase in fine particle concentrations in air pollution has been observed, exposure to fuels used for domestic heating and cooking could explain the occurrence of lung cancer in women", according to the study.
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The establishment of cancer registries
Indeed, the highest incidences of adenocarcinoma attributable to air pollution were found in East Asia, particularly in China. While the authors caution that their results should be interpreted with caution, given some methodological limitations and the variable availability of data across countries, they believe that their study highlights the need for continued monitoring of changes in lung cancer risk.
Especially since while lung cancer incidence rates in men have decreased in most countries over the past 30 to 40 years, they have increased in women.
"These divergent trends according to gender" must guide “Cancer prevention specialists and policy makers” towards “tobacco and air pollution control strategies tailored to high-risk populations”, says IARC researcher Freddie Bray, who led the study. The authors also call for cancer registries and for exploring the role of air pollution, where smoking is not considered the main cause of the disease.
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