Chemical composition of fine particulate matter and all-cause mortality of older lung cancer patients.
Ambient fine particulate matter (PM2.5) is a proven human lung carcinogen associated with lung cancer incidence. However, the relative toxicity of the various chemical components of PM2.5 and their joint association with all-cause mortality following lung cancer diagnosis remain unclear. We conducted a cohort study of 528,127 adults aged ≥65 years with lung cancer diagnosed between 2000-2019, derived from the SEER-Medicare database. Patients were followed annually from diagnosis until death, loss to follow-up, or end of the study in 2019. Two-year moving average exposures to 15 PM2.5 chemical components were estimated using high-resolution spatiotemporal models and linked to each patient based on residential ZIP code in each year. We used generalized weighted quantile sum regression with random holdouts to estimate both the joint association of PM2.5 component mixtures with all-cause mortality and the relative contribution of each component, adjusted for demographics, histological type, stage, first-course treatments, comorbidities, and neighborhood-level covariates. We found that joint exposure to PM2.5 component mixtures was associated with increased mortality, with relative risk of 1.011 (95% confidence interval [CI]: 1.010, 1.013) per decile increase in all components. Although differences in contributions were modest, silicon, nitrate, vanadium, zinc, and iron appeared to be more influential contributors, suggesting that controlling related sources, such as road dust, traffic emissions, fossil fuel combustion, and heavy fuel oil combustion, may obtain greater potential benefits. Exploratory subgroup analyses suggested that the joint association may be stronger among patients with non-small cell lung cancer, those with later-stage disease, and female patients.