Relationship between air pollution and lung cancer in nonsmokers – is there one?

For never-smokers (smoked <100 lifetime cigarettes), lung cancer  has emerged as an important issue. We aimed to investigate the effects of prevalence changes in tobacco smoking and particulate matter levels on lung cancer in Taiwan, in relation to contrasting particulate matter levels, between Northern Taiwan and Southern Taiwan.

In the United states and in other countries where tobacco smoking has been common it was previously thought that 90% of lung cancer resulted solely from cigarette smoking, however, in 2016, Whiteman and Wilson revealed that the global tobacco population attributable fraction was high in men (81%) but markedly lower in women (58%). According to the GLOBOCAN 2012 study, the relatively high rate of lung cancer in east Asian women is of particular interest because tobacco smoking is generally rare in these populations. Compared to lung cancer rates among smokers, lung cancer in those who have never smoked is associated with patients of east Asian descent, females, and those with an adenocarcinoma lung cancer histology.This population is more likely to have distinct molecular markers, especially EGFR, ALK receptor tyrosine kinase (ALK), and ROS1 gene mutations. Comprehensive genomic analysis using whole-genome sequencing has identified significant differences between the tumor genome of lung cancer in patients who have never smoked and smokers. Particulate matter air pollution contributes to the incidence of adenocarcinoma lung cancer in Europe, but the corresponding effect in East Asia is uncertain. In Taiwan, there have been differences in air pollution trends between Northern and Southern  Taiwan for approximately 25 years. Using both the Taiwan National Lung Cancer database Adult Smoking Behavior Surveillance System and the long-term nationwide visibility data, we aimed to investigate the effect of air pollution level changes on lung cancer rates in Taiwan, where there is a high prevalence rate of lung cancer among patients who have never smoked.

Methods of testing the relationship of air pollution and lung cancer

We reviewed 371,084 patients with lung cancer to assess smoking prevalence and correlations between the incidence of adenocarcinoma lung cancer and non-adenocarcinoma lung cancer. Two subsets were selected to assess different adenocarcinoma lung cancer stage trends and the effect of particulate matter levels on survival of patients with adenocarcinoma lung cancer.

Results

From 1995 to 2015, the proportion of male adult ever-smokers decreased from 59.4% to 29.9% whereas the female smoking rate remained low (3.2% to 5.3%). Adenocarcinoma lung cancer incidence in males and females increased from 9.06 to 23.25 and 7.05 to 24.22 per 100,000 population, respectively. Since 1993, atmospheric visibility in Northern Taiwan improved (from 7.6 to 11.5 km), but deteriorated in Southern Taiwan (from 16.3 to 4.2 km). The annual percent change in adenocarcinoma lung cancer stages IB to IV was 0.3% since 2009 in Northern Taiwan, and 4.6% since 2007 in Southern Taiwan; 53% patients with lung cancer had never smoked. Five-year survival rates for never-smokers, those with EGFR wild-type biomarkers and female patients with adenocarcinoma lung cancer were 12.6% in Northern Taiwan and 4.5% in Southern Taiwan.

Conclusions

In Taiwan, greater than 50% of patients with lung cancer had never smoked. Particulate matter levels changes can affect adenocarcinoma lung cancer incidence and patient survival.

Read the full article in the Journal of Thoracic Oncology, May 2019 issue.