Globally, lung cancer is the leading cause of cancer mortality in both men and women. The worldwide burden of lung cancer is substantial and projected to rise during the coming years, especially in East Asian countries, such as, the People’s Republic of China, Japan, South Korea, and Taiwan, because of the large population size, high incidence rates in males, and marked upward trend in incidence in females.1,2 The proportion of lung cancer in people who have never smoked has been increasing steadily in these countries.3 In some Asian countries, the incidence of lung adenocarcinoma has also been increasing over time, despite a steady decline in male smoking since the 1990s and a constant low smoking rate among females.4 As a separate entity, lung cancer in never smokers is the seventh leading cause of cancer deaths in both sexes worldwide.5
Traditionally, exposure to secondhand smoke (SHS), workplace carcinogens, residential radon, air pollution, diesel exhaust, cooking and heating fumes, arsenic in drinking water, or genetic susceptibility is thought to increase the risk of lung cancer in never smokers.4,5 SHS is a relatively weak carcinogen and can only account for a few of lung cancers arising in never smokers.5,6 In 2013, the International Agency for Research on Cancer revealed that outdoor air pollution and one of its major components, particulate matter (PM), specifically PM2.5, are important causes of lung cancer.7,8 The most recent Global Burden of Disease report estimated that 265,000 lung cancer deaths were attributed to outdoor air pollution in 2017 (14% of all lung cancer deaths).9 Despite the importance of ambient air pollution exposure as a lung cancer risk factor, cumulative exposure to particulate matter at the individual level in relation to sex and race or ethnicity has not been studied in patients with lung cancer. The purpose of this study was to compare the air pollution exposure in never smokers with lung cancer versus ever smokers with lung cancer, adjusting for sex, race/ethnicity, and additional factors.
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