Exposure to air pollution after a diagnosis of lung cancer can negatively affect survival, according to a new study published online August 4 in Thorax.
The effect was most pronounced for patients with early-stage disease, and in particular those with adenocarcinoma, which accounts for 80% of lung cancer cases.
In a population-based study of more than 352,000 patients with newly diagnosed lung cancer, higher exposure to nitrogen dioxide (NO2) and particulate matter of less than 10 microns in aerodynamic diameter (PM10) and less than 2.5 (PM2.5) was associated with shorter survival.
These observed associations were clinically significant, note the authors, led by Sandrah P. Eckel, PhD, assistant professor in the Division of Biostatistics at the University of Southern California in Los Angeles.
There was an increased risk for death (≤38%, dependent on cancer stage and pollutant), suggesting that “reductions in exposure have the potential to improve lung cancer survival,” they write.
Speaking in a BMJ podcast interview, Jaime E. Hart, ScD, from the Channing Division of Network Medicine, Brigham and Women’s Hospital and Harvard Medical School in Boston, Massachusetts, noted that the findings from the study were “a little surprising.”
“Before this study, there was very little evidence of the impact of air pollution on survival in individuals with lung cancer,” said Dr Hart, who is also the author of an accompanying editorial published in the same issue.
“The most interesting findings were that the impacts of pollution were very different by stage and histology at diagnosis, and the impact was strongest among those who traditionally have the highest survival rate,” she said.
While the results of this study aren’t conclusive, Dr Hart pointed out that this paper suggests patients with lung cancer may be particularly affected by air pollution. “The effect size was higher than in the general population, so it suggests that they may be more susceptible,” she said.
However, this is the first study to show this effect, and so “we have to be a little cautious in interpreting it.” Ideally, the results should be replicated, and Dr Hart noted that she would like to see a study that included information about patient behavior patterns, which was impossible to tease out in the current paper because the information came from a database.
Despite its limitations, such as being unable to account for potential confounding by changes in lifestyle habits or subsequent treatments, the study provides “compelling evidence that air pollution may be a potential target for future prevention and intervention studies to increase cancer survival,” writes Dr Hart in her editorial.
Overall, this study adds to the immense weight that current levels of air pollution are affecting health, she added.
Early Stage Most Affected
Underlying the study is the authors’ hypothesis that, if ambient air pollution can influence the development of lung cancer, then inhaled pollutants may also drive tumor progression “through the same mechanistic pathways to shorten survival after diagnosis.”
To address that question, Dr Eckel and colleagues conducted a population-based cohort study that included 352,053 California residents who were newly diagnosed with lung cancer from 1988 to 2009.
They estimated the average residential exposures to air pollutants from diagnosis to the end of follow-up, and this information was applied to all-cause mortality and lung cancer–specific mortality by stage and tumor histology at the time of diagnosis.
More than half of lung cancers (53%) were diagnosed at an advanced stage, and 324,266 patients died (92.1%) during the study period.
The authors used four different air pollution measures (PM10, PM2.5, NO2, and ozone), which were calculated by using data from US Environmental Protection Agency air quality monitoring stations and then mapped to the residential addresses of each individual at the time of diagnosis.
They also calculated the distance to the nearest highways to account for exposures to local traffic, and they included area-level information on measures of urbanicity and socioeconomic status.
Just under half of the cohort (45.4%) lived more than 1500 meters away from a major interstate highway, and only 8.7% lived within a 300-meter radius of one.
There was a pattern of shorter median and 5-year survival for patients with local or regional-stage disease who had higher exposure to NO2, PM10, or PM2.5.
As an example, the median survival for patients with local disease was 2.4 years if they had high PM2.5exposures (≥16 μg/m3) and 5.7 years for low PM2.5 exposures (<10 μg/m3).
Across all types of pollutants, the authors observed larger hazard ratios for patients diagnosed at earlier stages, and the effects of the various pollutants seemed to be greater for patients with adenocarcinoma than patients with small-cell cancer at the same stage.
Survival for patients with distant stage at diagnosis was poor, regardless of exposure to air pollutants.
The study was supported by the Southern California Environmental Health Sciences Center; the Hastings Foundation; the National Cancer Institute’s Surveillance, Epidemiology and End Results Program; and the Centers for Disease Control and Prevention’s National Program of Cancer Registries. The study authors and editorialist have disclosed no relevant financial relationships.