Long-term exposure to wildfire smoke PM2.5 and survival of older lung cancer patients—a retrospective, registry-based cohort study

Abstract

Summary Background Fine particulate matter (PM2.5) has been identified as a key risk factor of lung cancer incidence and survival. PM2.5 from wildfire smoke is an increasingly important contributor to total PM2.5 in the United States driven by climate change and potentially more toxic than non-wildfire PM2.5 due to its smaller particle size and higher toxic contents. However, its effects on survival of patients with lung cancer remain unclear. Methods This cohort study included patients ≥65 years with histologically confirmed primary small cell lung cancer (SCLC) or non-small cell lung cancer (NSCLC), as defined by the International Classification of Diseases for Oncology, Third Edition (ICD-O-3), from SEER-Medicare database (01/01/2006–31/12/2019), with residential zip code-based estimates of wildfire smoke and non-wildfire PM2.5. A time-varying Cox proportional hazards model was applied to estimate the long-term effects of three-year moving averages of wildfire smoke PM2.5 and non-wildfire PM2.5 concentrations on overall survival. Findings A total of 414,016 patients contributed 1,211,490 person-years of follow up during the analysis period (01/01/2008–31/12/2019), with a median follow-up of 2 years (interquartile range [IQR] 1–4 years). Of these, 208,468 (50.4%) were female and 205,548 (49.6%) were male. In terms of race/ethnicity, 356,356 (86.1%) were White, 36,914 (8.9%) were Black, 18,982 (4.6%) were Asian or Pacific Islander, and 1,269 (0.3%) were American Indian or Alaska Native; race was unknown for 495 participants (0.1%). The median concentrations of wildfire smoke PM2.5 and non-wildfire PM2.5 were 0.28 (IQR 0.21–0.39) and 8.11 (IQR 6.84–9.47) μg/m3, respectively. Each 1-SD increase in wildfire smoke PM2.5 and non-wildfire PM2.5 was associated with a 2.29% (HR 1.0229, 95% CI 1.0189–1.0270, p<0.0001) and 3.84% (HR 1.0384, 95% CI 1.0335–1.0432, p<0.0001) higher risk of death among lung cancer patients, respectively. Notably, the mortality risk per 1-μg/m3 increase was substantially greater for wildfire smoke PM2.5 (HR 1.0782, 95% CI 1.0641–1.0924, p<0.0001) than of non-wildfire PM2.5 (HR 1.0171, 95% CI 1.0149–1.0192, p<0.0001). Overall, approximately 700 and 3,470 average annual excess deaths in our cohort were attributable to wildfire smoke and non-wildfire PM2.5, respectively. Interpretation Wildfire smoke PM2.5 exhibits greater toxicity per unit exposure and is the fastest-growing contributor to ambient air pollution, underscoring the urgent need for updated wildfire management and mitigation strategies. Funding NIEHS; NCI; NIH; NCATS; CDC(NPCR); Stony Brook University.