Chemical composition of fine particulate matter and mortality of older lung cancer patients

Importance: Lung cancer mortality remains elevated despite advances in treatment. Although ambient fine particulate matter (PM 2.5 ) has been identified as Group 1 carcinogen for lung cancer, which increases the incidence, the role of chemical components in mortality of lung cancer patients and the identification of harmful components and susceptible groups remain unclear. Objective: To evaluate whether long-term exposure to PM 2.5 chemical components is associated with all-cause mortality among lung cancer patients, and whether the associations differ by histology and stage at diagnosis, demographics, and comorbidity. Design, Setting, and Participants: This cohort study derived from the SEER-Medicare database that identifed 495,339 adults aged ≥65 years with lung cancer diagnosed between 2000 and 2019. Patients were followed annually from diagnosis until death, loss to follow-up, or the end of 2019 (mean follow-up, 4.1 years). The SEER-Medicare database provided longitudinal residential ZIP code, demographics, cancer-specific characteristics, and comorbidities. Exposures: Annual exposures to 15 PM 2.5 chemical components were estimated from 2000 to 2019 using high-resolution spatiotemporal models and linked to each patient based on residential ZIP code in each year. Main Outcome: The primary outcome was the relative risk of all-cause mortality, measured from the year of lung cancer diagnosis until death or the end of follow-up. We used generalized weighted quantile sum regression to estimate both cumulative effects of annual exposure to all components and individual contributions for each component, adjusted for demographic, cancer-specific characteristics (histology, stage, treatment), comorbidities, and neighborhood-level covariates. Results: Joint exposure to PM 2.5 components was associated with increased all-cause mortality, with relative risk [RR] being 1.012 (95% confidence interval [CI], 1.011-1.014) per decile increase in all components. Iron contributed most strongly (8.3% of total effects), followed by organic carbon, vanadium, ammonium, bromine, and silicon. Associations were stronger among patients with non-small cell lung cancer, particularly squamous cell carcinoma, as well as among women and those with regional-stage disease. Conclusions and Relevance: Long-term exposure to PM 2.5 components was linked to greater mortality among patients with lung cancer, especially in those diagnosed with non-small cell and squamous cell carcinoma, women, and with advanced stage. Chemical components that contributed most to this effect emitted from traffic, power generation, biomass burning, and heavy fuel oil, highlighting the need for targeted emission reductions to improve outcomes in high-risk populations.