Long-term exposure to wildfire smoke PM 2.5 and survival of older lung cancer patients

Importance Fine particulate matter (PM 2.5 ) is a key risk factor of lung cancer incidence and mortality. However, the specific effect of PM 2.5 originating from wildfire smoke, an increasingly important contributor to total PM 2.5 in the US driven by climate change, on mortality of patients with lung cancer remain unclear. Objective To explore the effect of long-term exposure to wildfire smoke versus non-smoke PM 2.5 on all-cause mortality of older lung cancer patients. Design, Setting, and Participants This cohort study included patients ≥65 years with primary diagnosis of lung cancer from the SEER-Medicare database from 2006 to 2019 linked with estimates of exposure to wildfire smoke and non-smoke PM 2.5 based on patients' residential zip codes. Exposures Three-year moving average exposures to wildfire smoke and non-smoke PM 2.5 . Main Outcomes and Measures The study outcome was all-cause mortality after primary lung cancer diagnosis. A time-varying Cox proportional hazards model was applied to estimate hazard ratios (HRs) for mortality risk. Results Among 503,409 patients with 1,542,491 person-years of follow up, each 1-μg/m³ increase in wildfire smoke PM 2.5 was associated with a 9.3% increased mortality risk (HR: 1.09, 95% CI: 1.08-1.11), substantially greater than that of non-smoke PM 2.5 (HR: 1.020, 95% CI: 1.018-1.022). The number of smoke days and of smoke waves, reflecting duration and frequency of wildfire smoke PM 2.5 exposure, were also positively associated with mortality risk. Larger effect of wildfire smoke PM 2.5 was observed among women, patients with lung cancer other than non-small cell lung cancer, patients with comorbidities, and those not receiving first course treatment after diagnosis. Conclusions Wildfire smoke posed a substantially larger risk in older lung cancer patients than non-smoke PM 2.5 . Under a changing climate, strengthening wildfire management and reducing wildfire smoke exposure in clinical care could improve survival of older lung cancer patients. HR for mortality and corresponding annual excess deaths associated with smoke and non-smoke PM2.5 Three-year moving average wildfire smoke PM 2.5 exposure Hazard ratio (95% CI) Annual excess deaths (95% CI) Concentration, per 1-μg/m 3 increase Smoke PM 2.5 1.0927 (1.0801, 1.1055) 2,908 (2,513, 3,310) Non-smoke PM 2.5 1.0202 (1.0182, 1.0222) 634 (571, 696) Smoke-event duration and frequency, per day/event increase Number of smoke days 1.0040 (1.0037, 1.0043) 125 (116, 135) Number of smoke waves 1.0209 (1.0185, 1.0233) 656 (580, 731)