Increase in Lung Cancer Diagnoses Among Non-Smokers Globally

 Research Highlights the Need for Further Studies on Air Pollution and Other Contributing Factors

The number of people diagnosed with lung cancer who have never smoked is on the rise, with air pollution identified as a significant factor, according to the World Health Organization’s cancer agency.

Lung cancer among individuals who have never used cigarettes or tobacco is now estimated to be the fifth leading cause of cancer-related deaths worldwide, as reported by the International Agency for Research on Cancer (IARC).

The IARC noted that nearly all cases of lung cancer in non-smokers manifest as adenocarcinoma, which has become the most prevalent of the four primary lung cancer subtypes in both men and women globally.

A study published in The Lancet Respiratory Medicine journal indicated that in 2022, approximately 200,000 adenocarcinoma cases were linked to air pollution exposure. The highest incidence of adenocarcinoma attributed to air pollution was recorded in East Asia, particularly in China.

Dr. Freddie Bray, the study’s lead author and head of the IARC’s cancer surveillance branch, emphasized the urgent need to monitor the evolving risk of lung cancer. Speaking to The Guardian, he highlighted the necessity for further research to identify causal factors like air pollution in populations where smoking is not the primary cause of lung cancer.

Bray explained that as smoking rates decline such as in the UK and US the proportion of lung cancer diagnoses among non-smokers tends to increase. He noted that whether adenocarcinomas caused by air pollution will continue to rise globally depends on the effectiveness of future efforts to reduce tobacco consumption and air pollution.

Lung cancer remains the most commonly diagnosed and fatal cancer worldwide. In 2022, around 2.5 million people were diagnosed with the disease. However, the incidence patterns by subtype have shifted significantly over the past few decades.

Among the four primary subtypes adenocarcinoma, squamous cell carcinoma, small-cell carcinoma, and large-cell carcinoma adenocarcinoma has emerged as the most common type in both men and women, according to the IARC.

In 2022, adenocarcinoma accounted for 45.6% of lung cancer cases among men and 59.7% among women, compared to 39.0% and 57.1%, respectively, in 2020. Additionally, the IARC reported that adenocarcinoma represents up to 70% of lung cancer cases in never-smokers.

While lung cancer incidence rates in men have generally declined over the past 40 years, rates among women have continued to rise. Current trends indicate that although men still account for the majority of lung cancer cases (around 1.6 million in 2022), the gap between male and female incidences is narrowing, with approximately 900,000 women diagnosed in the same year.

In 2023, The Guardian reported that, for the first time, the number of women diagnosed with lung cancer in the UK had surpassed that of men. This development has led to calls for increased vigilance among women regarding lung cancer, similar to awareness efforts for breast cancer.

Experts attribute these figures to historical differences in smoking prevalence, noting that smoking rates peaked earlier in men than in women. They stress that women should be as attentive to potential lung cancer symptoms as they are to signs of breast cancer.

The IARC stated that changes in cigarette manufacturing and smoking behaviors over recent decades have influenced lung cancer incidence trends by subtype. Furthermore, growing evidence suggests a causal link between air pollution and a heightened risk of adenocarcinoma.

Although the exact proportion of global lung cancer cases among non-smokers is not yet determined, available data indicate an upward trend. Researchers are working to understand additional causes of lung cancer beyond smoking.

The study underscored that air pollution is a significant factor in the increasing prevalence of adenocarcinoma, accounting for 53% to 70% of lung cancer cases among never-smokers worldwide.

Bray emphasized that the research offers valuable insights into the evolving nature of lung cancer and its risk factors, shedding light on effective prevention strategies.

He concluded, "Shifts in smoking habits and exposure to air pollution are among the key factors shaping the changing risk profile of lung cancer by subtype. The differing trends between men and women in recent generations provide crucial insights for cancer prevention experts and policymakers aiming to design and implement tobacco and air pollution control strategies tailored to high-risk populations."