Exposure to air pollution during pregnancy and the first year of life might increase the likelihood of developing certain childhood cancers, California researchers say.
Researchers from the University of California, Los Angeles School of Public Health collected data on children diagnosed with cancer before the age of 6 and local traffic exposure. The greater the traffic pollution, the higher the odds for acute lymphoblastic leukemia (white blood cell cancer), germ cell tumors (cancers of the testicles, ovaries and other organs) and eye cancer, they found.
These findings do not mean pollution actually causes these cancers, said lead researcher Julia Heck, an assistant researcher in the department of epidemiology. "This finding is an association, because nothing is proven yet," she said.
But the results do suggest that exposure to traffic pollution might increase risk for childhood cancers, Heck added. "Since this was the first study to report risks for these [uncommon childhood] cancers, these findings need to be confirmed in other studies," she said.
Areas of California are known for their unhealthy air. The state's topography and its warm, sunny climate tend to form and trap air pollutants, creating smog, according to the California Air Resources Board.
The researchers focused on pregnancy because certain cancers originate in the womb, Heck said.
But women shouldn't worry about their baby's risk for cancer based on this study, another expert said.
"There has been an association between air pollution and other diseases," said Dr. Rubin Cohen, director of the Adult Cystic Fibrosis and Bronchiectasis Center at the Long Island Jewish Medical Center in New Hyde Park, N.Y. "We know that pollution causes asthma, and that is probably more real than the cancer issue."
Cohen isn't sure the association between pollution and childhood cancers is causal, and he said there isn't much one can do about it anyway. "Moving is easier said than done," he said.
The study findings were scheduled for presentation Tuesday at the annual meeting of the American Association for Cancer Research in Washington, D.C.
For the study, Heck's team collected data on nearly 3,600 children under 6 years old who were born between 1998 and 2007 and listed in the California Cancer Registry. The researchers compared them with a similar number of healthy children.
The researchers were able to estimate the amount of traffic pollution at each child's home during the mother's pregnancy and the child's first year of life. The estimates included exposure to gas and diesel engines as well as traffic volume, emission rates and weather.
Based on their findings, Heck's group concluded the risk for cancer was increased with higher exposure to vehicular air pollution. "In terms of the risk, greater exposure was associated with a 5 percent increase in [acute lymphoblastic leukemia] cancers, an 11 percent increase in eye cancer and a 15 percent increase in testicle, ovary and other organ tumors," Heck said.
But whether any particular period is critical during pregnancy or the child's first year wasn't clear.
Another expert agreed that more research is needed before conclusions can be drawn about any actual risk for cancer from traffic pollution.
The study needs to be replicated to see if the same findings are seen in other cities, said Dr. Guillermo DeAngulo, a pediatric oncologist at Miami Children's Hospital, in Florida.
"There has been a concern about environmental factors playing a role in cancers," said DeAngulo, who was not involved in the study. "The question is how much of a role they play."
Genetic components also may be involved that may make cancer more likely for some of these children, he said.
Data and conclusions presented at meetings are typically considered preliminary until published in a peer-reviewed medical journal.