Wildfire smoke exposure was linked to shorter survival in older people with lung cancer

Design

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

Population

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

Primary outcome

All-cause mortality by 3-year average PM2.5 exposure

Effect

Wildfire-related PM2.5 HR 1.0782 per 1 microgram/m3 (95% CI 1.0641 to 1.0924); non-wildfire 1.0171 (1.0149 to 1.0192)

A retrospective SEER-Medicare cohort included 414,016 patients aged 65 or older with lung cancer, diagnosed 2008 to 2019, contributing 1.2 million person-years. Residential zip code estimates of wildfire-related and other fine particulate matter (PM2.5) were averaged over three years and linked to all-cause mortality with time-varying Cox models.

Each standard deviation increase in wildfire-related PM2.5 was associated with a hazard ratio for death of 1.0229 (95% CI 1.0189 to 1.0270), and for non-wildfire PM2.5, 1.0384 (1.0335 to 1.0432). Per 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 other PM2.5, which suggests more harm per unit from wildfire smoke. About 696 average annual excess deaths were attributed to wildfire-related PM2.5 and 3,465 to the rest.

This is an ecological exposure assigned by zip code in a US population, with residual confounding by smoking and socioeconomic factors likely. The effect sizes are small, and median follow-up was two years. The finding is relevant in India for air pollution generally, but its numbers do not transfer.

• Ask about air quality, cooking fuel and occupation as part of the exposure history in lung cancer
• Advise limiting outdoor activity on high-pollution days for patients with lung cancer
• Do not use the hazard ratios to predict an individual patient's prognosis
• Consider air pollution as a modifiable background factor when discussing survivorship

Why it matters

It suggests air pollution matters not only for getting lung cancer but for surviving it.

Don't overread it

This is an observational association from US registry data and cannot show that reducing exposure would improve an individual's survival.

The statistics, in plain English

Hazard ratios of 1.02 to 1.08 per unit of exposure are small individually but add up across millions of person-years. They reflect average associations across populations, and the exposure estimates are modelled from satellite and monitor data for each zip code, not personally measured.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.