Wildfire smoke particles and survival in older patients with lung cancer

Design

Retrospective registry-based cohort (SEER-Medicare), time-varying Cox models

Population

414,016 patients aged 65 or over with lung cancer, diagnosed 2008 to 2019

Primary outcome

All-cause mortality

Effect

Wildfire-related PM2.5 HR 1.0782 per microgram per cubic metre (95% CI 1.0641 to 1.0924); non-wildfire 1.0171 (95% CI 1.0149 to 1.0192)

Using US cancer registry linked to Medicare data, this retrospective cohort followed 414,016 patients aged 65 or over with small-cell or non-small-cell lung cancer diagnosed between 2008 and 2019 (median follow-up 2 years). Residential estimates of fine particulate matter were split into wildfire-related and non-wildfire sources, as three-year moving averages.

Each standard-deviation increase in either was associated with a higher risk of death: HR 1.0229 (95% CI 1.0189 to 1.0270) for wildfire-related and 1.0384 (1.0335 to 1.0432) for non-wildfire particles. Per 1 microgram per cubic metre the hazard ratio was 1.0782 (1.0641 to 1.0924) for wildfire-related and 1.0171 (1.0149 to 1.0192) for non-wildfire particles, suggesting more harm per unit from wildfire smoke. The authors estimate about 696 average annual excess deaths from wildfire-related and 3,465 from non-wildfire particles in this cohort.

The design is observational, exposure is estimated at postcode level and not measured in individuals, and residual confounding by socioeconomic factors is possible. It concerns US conditions, while exposure in India comes from other sources such as traffic, biomass and crop burning. The finding supports advising patients on reducing exposure to smoke and polluted air.

• Ask patients with lung cancer about household and ambient smoke exposure, including biomass cooking fuel.
• Advise limiting outdoor activity and using masks or filtered air when pollution is high, where practical.
• Support smoking cessation and clean cooking fuel alongside cancer treatment.
• Do not state air quality as a proven cause of shorter survival in an individual patient.

Why it matters

It suggests the source of air pollution may matter, not just its level.

Don't overread it

This is an observational study with area-level exposure estimates in the United States; it does not show how much air pollution shortens an individual's survival.

The statistics, in plain English

A hazard ratio of 1.078 per microgram per cubic metre means about 8% higher mortality for each unit of wildfire-related particles, a much larger step than for other particles per unit. The absolute concentrations of wildfire particles were low (median 0.28 micrograms per cubic metre), so the overall effect on a person depends on how much their exposure rises.

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