A population-based study published in Thorax suggests that air pollution may worsen survival outcomes for patients with lung cancer.1 The impact of air pollution on survival rates was most pronounced among patients with early stage disease and adenocarcinoma in particular.

The International Agency for Research on Cancer in Lyon, France classified ambient air pollution as carcinogenic in 2013.2 The effects of pollution on survival after diagnosis were, however, unclear.

“We reasoned that if air pollution drives lung cancer development, it could affect lung cancer progression—and shorten survival—through the same biological pathways,” said study co-author Sandy Eckel, PhD, of the University of Southern California in Los Angeles, in an email to Cancer Therapy Advisor.

“There is a growing body of evidence that ambient air pollution exposures are linked to lung cancer incidence and mortality, but due to the high case-fatality rate, few studies have attempted to disentangle the 2.”

Dr Eckel and colleagues analyzed the health outcomes of more than 352,000 patients in the US California Cancer Registry who were newly diagnosed with lung cancer between 1988 and 2009. More than half of the patients were diagnosed with advanced cancer, the average survival time for which was 4 months. The average survival time for early stage cancer was 3.6 years.

More than 45% of patients lived further than 1500 meters from a large interstate highway, while less than 10% lived within 300 meters of 1. Higher exposures to each of 4 pollutants were associated with higher risk of death and worse 5-year survival rates.

“It was interesting that we found some of the strongest associations between air pollution exposures after diagnosis and survival among patients diagnosed with early stage adenocarcinoma,” said Dr Eckel. “Adenocarcinoma is the most common histological subtype of lung cancer in non-smokers.”

In an accompanying editorial, Jaime Hart, ScD, of the Brigham and Women’s Hospital and Harvard Medical School in Boston, Massachusetts, wrote that while the Thorax study “provide[s] compelling initial evidence that air pollution may be a potential target” for future studies, it “does have limitations.”3

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Dr Hart noted that unaccounted lifestyle changes by patients may offer “potential for confounding.” She also raised concerns about the accuracy of the study’s measure of patient exposure to pollutants, and wrote that “future studies should improve on the exposure accuracy of the current analysis with the use of residence-level or individual-level predictions.”

Dr Eckel agrees that causal relationships are not yet established. “The associations in this study are suggestive, but do not demonstrate a cause and effect. More research is needed to replicate these findings before they can be translated into clinical practice.”

References

  1. Eckel SP, Cockburn M, Shu YH, et al. Air pollution affects lung cancer survival. Thorax. 2016 August 4. doi: 10.1136/thoraxjnl-2015-207927 [Epub ahead of print]
  2. IARC: Outdoor air pollution a leading environmental cause of cancer deaths. International Agency for Research on Cancer. https://www.iarc.fr/en/media-centre/iarcnews/pdf/pr221_E.pdf. Updated October 17, 2013. Accessed August 21, 2016.
  3. Hart JE. Air pollution affects lung cancer survival. Thorax. 2016 August 4. doi: 10.1136/thoraxjnl-2016- 208967 [Epub ahead of print]