Exposure to wildfire smoke may increase lung cancer patients' risk of dying from their disease, particularly among non-smokers, but the effect may be mitigated by certain cancer treatments, according to a large California study presented at a major medical meeting on Saturday.

Researchers tracked more than 18,000 people with non-small cell lung cancer – the most common kind – between 2017 and 2020. Those living in neighborhoods with the highest levels of wildfire-caused air pollution in the year after their cancer diagnosis were more likely to die from the disease, they found.

Patients who inhaled higher levels of tiny particulate matter with a diameter of 2.5 microns or less that can penetrate deeply into the lungs had a 20% greater risk of dying from lung cancer, researchers reported at the American Society of Clinical Oncology meeting in Chicago.

People with advanced stage 4 cancer who had never smoked were especially affected, researchers found. Their risk of dying from cancer was 55% higher if they were exposed to high levels of wildfire air pollution.

The study used advanced modeling to estimate daily air quality at patients’ home addresses, based on data from satellites, weather models, smoke forecasts and air quality monitors.

The researchers also found that wildfire smoke exposure did not significantly affect survival of patients with Stage 4 lung cancer with a history of smoking who were treated with an immunotherapy drug.

“This surprising trend suggests that smoke-related changes in the body may interact with certain treatments,” and more study of this phenomenon is warranted, the researchers said.

Wildfire smoke is more toxic than normal air pollution. Along with particles of soil and biological materials, it often contains traces of chemicals, metals, plastics and other synthetic materials.

“As wildfires become more frequent and intense in California and other parts of the US, we need targeted health strategies to protect cancer patients and others with serious health problems,” said study leader Dr Surbhi Singhal of UC Davis Comprehensive Cancer Center in Sacramento, California.