Wildfire season used to feel like a short, scary stretch of the year. Now it hangs over whole regions for months. Smoke settles into cities, creeps inside houses, and makes everyone cough. But for people living with or after cancer, that haze may be far more dangerous than most of us realize.
A new study published in Cancer Epidemiology, looked at more than seven million cancer patients across the United States. Yes, seven million. The researchers wanted to understand a simple but important question: Does long-term exposure to dirty air affect how long cancer survivors live? And even more specifically, what happens when that dirty air comes from wildfires?
The team focused on PM2.5, a type of air pollution comprised of fine particles so tiny it slips deep into the lungs. It’s already considered a cancer-causing substance. We breathe it in all the time from cars, industrial plants, and now, huge fires., but very little research has examined carefully how it affects people after they’ve had cancer.
Dr. Trang VoPham, an Associate Professor in the Epidemiology Program and the lead author explained: “The number of cancer survivors is rapidly increasing, and these individuals may be particularly vulnerable to the harmful effects of environmental exposures because of treatment-induced physiological changes and other factors.” It makes sense when you think about it. Cancer treatment is tough on the body. Even years later, it can leave people with weakened immune systems or lingering inflammation. So, breathing polluted air isn’t just unpleasant; it may be downright dangerous.
The study found that higher PM2.5 exposure was linked with an increased risk of earlier mortality among cancer survivors. That was true for cancer-specific outcomes and for overall survival. And the story didn’t end there. The risk got even stronger in places that deal with a lot of wildfires. “We observed that among cancer patients, the association between ambient fine particulate matter air pollution (PM 2.5) and cancer mortality was stronger among those residing in areas more heavily impacted by wildfires,” Dr. VoPham said. In other words, the same amount of pollution seems more dangerous when it’s shaped by wildfire smoke.
The researchers also wanted to know who might be most affected. Older adults, people with cancers not related to smoking, and those who hadn’t received treatment showed even stronger links between pollution and mortality. It’s a reminder that health risks aren’t evenly shared. They layer on top of each other depending on age, background, access to care, and even geography.
There’s something unsettling about the idea that your zip code could shape your survival after cancer. They even tested a few different ways of capturing wildfire exposure from how many fires burned in a county to how much land or how many people were affected, and no matter the measure, the same pattern held. But that’s exactly why this work matters. Wildfires are getting bigger. They’re happening more often. And as Dr. VoPham put it, “Extreme weather events, such as high temperatures, can increase the frequency, duration, and intensity of exposures to certain environmental hazards — one of which being wildfires.” The environment is shifting in ways that are already affecting the air people breathe today.
The researchers aren’t done and want to dig deeper. “We plan to follow up on our findings through examining more detailed information such as precise locations where individuals live and have moved over time,” Dr. VoPham explained. That kind of work could reveal whether certain moments of exposure, for example before diagnosis, during treatment, or after, matter more than others.
So, clean air isn’t just a nice idea. For millions of cancer survivors, it may literally be part of their lifeline. And as wildfire smoke becomes a regular feature of summers across the country, we’ve got to treat air quality like a core part of public health.
Fred Hutch/University of Washington/Seattle Children’s Cancer Consortium Members Drs. Trang VoPham, Jason Mendoza, Christopher Li contributed to this research.
This work was supported by the National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, National Cancer Institute, and National Institute of Environmental Health Sciences and the Dillon Family Foundation.
VoPham, T., Liu, T., Cortez, M., Karasaki, S., Falkenberg, N. F., Zewdie, H. Y., Lin, J., Nondin, C., Chao, S. L. S., Knowlton, T., Quennehen, B., Mendoza, J. A., Ioannou, G. N., Berry, K., Adamkiewicz, G., Li, C. I., & Hart, J. E. (2025). Exposure to outdoor air pollution, wildfires, and cancer survival in the United States. Cancer epidemiology, 98, 102899.
Science Spotlight writer Darya Moosavi is a postdoctoral research fellow within Johanna Lampe's research group at Fred Hutch. Darya studies the nuanced connections between diet, gut epithelium, and gut microbiome in relation to colorectal cancer using high-dimensional approaches.
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