Air quality has improved over the last 10 to 20 years thanks in part to stricter emission standards for motor vehicles; however, traffic-related air pollution may still contribute to several childhood cancers, according to research presented recently at the annual meeting of the American Association for Cancer Research in Washington, D.C. 1

Researchers from the Department of Epidemiology at the University of California, Los Angeles School of Public Health analyzed data on 3,950 children born between 1998 and 2007 who were enrolled in the California Cancer Registry and had been diagnosed with cancer at age 5 or younger. Controls were selected at random from children of the same age listed on California birth rolls. Exposure to pollution was calculated for each trimester of the mother’s pregnancy and during the first year of the child’s life by estimating gasoline- and diesel-powered traffic within 1,500 meters of the child’s home and analyzing roadway geometry, vehicle emission rates, and weather.

“The main reason for undertaking this study was that we know much more about the causes of adult cancers than we do of the causes of childhood cancers,” said Julia Heck, PhD, MPH, who led the study. “We studied pregnancy exposures because the fetus is likely to be vulnerable to environmental factors, and we also know that certain childhood cancers originate in utero.” 

Each interquartile range increase in exposure to traffic-related air pollution was associated with increased risk of three rare childhood cancers: acute lymphoblastic leukemia (4%), germ-cell tumors (17%), and retinoblastoma (14%).

Pollution-exposure estimates were similar throughout pregnancy and the first year of life, making it difficult to determine if exposure during a particular period carries extra risk. 

“Our innovation was looking at other, more rare types of childhood cancer, such as retinoblastoma, and their possible connection to traffic-related air pollution,” Dr. Heck said. She cautioned that the findings are preliminary and require replication. “It would be interesting to determine if there are specific pollutants like benzene or polycyclic aromatic hydrocarbons that are driving these associations,” she said.

Worldwide, air pollution is a significant and growing contributor to mortality, according to the 2010 Global Burden of Disease Study, which found that air pollution is currently the seventh-leading cause of death.2 It is likely to become the leading cause by 2050, according to a report in the New York Times.3

The disease burden of air pollution is especially high in developing countries such as China, where it contributes to about 20% of cases of lung cancer in China, according to Dr. Aaron Cohen, principal epidemiologist with the Health Effects Institute and co-chair of the Global Burden of Disease Ambient Air Pollution Expert Group, who spoke at an international workshop in Beijing on March 31. Air pollution also contributes to 1.2 million premature deaths in China each year, including 139,000 deaths from cancer of the trachea, bronchi, and lungs.4 More research, such as that conducted by the University of California, can further determine the impact of specific air pollutants.


References

1. Mason S. UCLA researchers find potential link between auto pollution, some childhood cancers. UCLA Newsroom. April 9, 2013. http://newsroom.ucla.edu/portal/ucla/ucla-researchers-link-auto-pollution-244911.aspx

2. Global Burden of Disease Study 2010. The Lancet. December 13, 2012. http://www.thelancet.com/themed/global-burden-of-disease

3. Air Pollution Linked to 1.2 Million Premature Deaths in China. The New York Times. April 1, 2013. http://www.nytimes.com/2013/04/02/world/asia/air-pollution-linked-to-1-2-million-deaths-in-china.html

4. Report: 1.2 mln Chinese Died from Air Pollution in 2010. GBTimes. December 4, 2012. http://gbtimes.com/focus/environment/news/report-12-mln-chinese-died-air-pollution-2010