Exposure to wildfire smoke was associated with a significantly increased risk of lung, colorectal, breast, bladder, and blood cancers, according to results from a study presented at the American Association for Cancer Research (AACR) Annual Meeting 2026 (Abstract 6252).
Although it’s known that wildfire smoke contains a wide array of toxins, including carcinogens like polycyclic aromatic hydrocarbons, the whole-body impacts of wildfire smoke in real-world settings remain unclear, especially when it comes to cancer incidence, according to Qizhen Wu, PhD, the study’s first author and a postdoctoral fellow at The University of New Mexico (UNM) Comprehensive Cancer Center.
Dr. Wu explained that the toxic compounds in wildfire smoke have the potential to disrupt a variety of biological systems—not just in the lungs, the site of initial exposure, but in the blood as well, which can then spread carcinogens throughout the body. He also noted that smoke exposure is itself an inflammatory event with systemic implications for carcinogenesis.
“Wildfires are becoming more frequent and severe in the United States and globally, and wildfire smoke has emerged as a major source of ambient air pollution, reversing decades of improvement achieved under the Clean Air Act,” said senior study author Shuguang Leng, MBBS, PhD, Associate Professor at the UNM Comprehensive Cancer Center. “The main purpose of our study was to examine whether long-term exposure to wildfire smoke was associated with the risk of developing cancer in the general population.”
PLCO Trial Analysis
Drs. Wu, Leng, and colleagues analyzed cancer incidence data from the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, which tracks the cancer incidence of adults from across the United States with no history of prostate, lung, colorectal, or ovarian cancers who enrolled between 1993 and 2001.
To quantify participants’ exposure to wildfire smoke, the researchers assessed the fine particulate matter (PM2.5) and black carbon from ground-level air pollution data sourced from participants’ residential areas. The team used satellite images from 2006 onward to match PM2.5 and black carbon data with wildfire smoke exposure events; they also used the satellite images to calculate the number of days that participants’ areas of residence were exposed to wildfire smoke plumes, defined as plume-day counts. The analysis accounted for wildfire smoke exposure monthly until a participant’s first cancer diagnosis or their last contact with the study.
Within the PLCO trial, 91,460 participants were evaluable for wildfire smoke exposure. From 2006 to 2018, the researchers calculated 36-month moving averages updated monthly for each participant’s exposure to wildfire smoke as defined by micrograms per cubic meter (µg/m3) for PM2.5 and black carbon and days of exposure for wildfire smoke plume-day counts. The median of those moving averages was 0.37 µg/m3 for wildfire smoke PM2.5, 0.0083 µg/m3 for wildfire smoke black carbon, and 1.94 days for monthly wildfire smoke plume-day counts.
During the same time period, the research team identified 1,758 lung cancer cases; 800 colorectal cancer cases; 1,739 breast cancer cases; 242 ovarian cancer cases; 896 bladder cancer cases; 1,696 blood cancer cases; and 1,127 melanoma cases.
Using a statistical analysis method that allows scientists to examine nonlinear risk associations, the researchers confirmed that wildfire smoke exposure was significantly associated with an increased risk of developing lung, colorectal, breast, bladder, and blood cancers. There was no evidence of deviation from a linear dose-response relationship. Associations with ovarian cancer and melanoma were not significant.
The team also found that the risk of developing these cancers increased with every additional 1 µg/m3 in the 36-month moving average of wildfire smoke PM2.5. Every 1 µg/m3 increase in wildfire smoke PM2.5 exposure was associated with significantly greater likelihoods of developing cancer: a 92% greater risk of lung cancer; a 131% greater risk of colorectal cancer; a 109% greater risk of breast cancer; a 249% greater risk of bladder cancer; and a 63% greater risk of blood cancers.
The associations between increased exposure levels and risk for various cancers were similar for wildfire smoke plume-day counts. However, the associations between increased wildfire smoke black carbon exposure and risk of cancer development were only significant for breast and bladder cancer.
“For the general public, the key message is that wildfire smoke is not only a short-term respiratory or cardiovascular concern—chronic exposure may also carry long-term cancer risks,” said Dr. Wu. “Notably, increased cancer risk may occur even at relatively low levels of wildfire smoke PM2.5 commonly experienced by general populations.”
Dr. Wu noted that further investigation was warranted for specific aspects of wildfire smoke, including its origin and its contents, which could have different implications for cancer risk across the continent depending on which geographic populations were exposed to which sources. Wildfires from different regions may contain different compounds from burning in varying proportions, and the chemical transformations that occur in smoke as it drifts may also impact biological effects, he said.
“As wildfires continue to increase in frequency and intensity, understanding their long-term health impacts is becoming increasingly important,” said Dr. Leng. “While more research is needed, we hope these findings will help raise awareness and support future studies on the long-term health effects of wildfire smoke.”
Limitations of this study include that data from satellite images are only available from 2006, which precluded analysis of wildfire smoke’s role in cancer initiation due to the sometimes yearslong delay between cancer initiation and cancer diagnosis. Additionally, the location-based analysis assumed that participants were located within their residential areas during every measured period of exposure and did not account for time spent indoors vs outdoors.
DISCLOSURE: This study was funded by the National Institutes of Health. For full disclosures of the study authors, visit abstractsonline.com.
