Exposure to outdoor air pollution, wildfires, and cancer survival in the United States

Abstract

Background

Climate change has led to an increase in wildfires, a major source of air pollution, which may be particularly harmful to individuals diagnosed with cancer. The objective of this study was to examine the relationships of air pollution and wildfires with mortality risk among cancer survivors.

Methods

Surveillance, Epidemiology, and End Results (SEER) cancer registries provided information on 7,051,014 patients diagnosed with cancer from 2000 to 2021 in the United States. Cox regression was used to calculate adjusted hazard ratios (HRs) and 95 % confidence intervals (CIs) for the associations between exposures to particulate matter < 2.5 µm (PM_2.5), nitrogen dioxide (NO₂), ozone (O₃), and wildfires (estimated using high-resolution geospatial datasets) with all-cause and cause-specific mortality risk.

Results

There were 3,452,593 deaths, including 2,369,364 from cancer, 525,409 from cardiopulmonary, and 557,820 from other causes. Among cancer survivors, higher exposure to PM_2.5 and wildfires (but not NO₂ or O₃) were associated with increased risk for all-cause, cancer, and other mortality. The association between PM_2.5 and cancer mortality was stronger in counties more heavily impacted by wildfires (HR per 10 μg/m³ in counties with ≥ median 0.39 wildfires per year: 1.17, 95 % CI 1.04–1.33) vs. no wildfires (HR 1.06, 95 % CI 0.97–1.15) (p interaction = 0.0064).

Conclusions

Among patients diagnosed with cancer, PM_2.5 air pollution, particularly in areas heavily impacted by wildfires, is associated with increased risk for mortality.