Traffic pollution may increase risk of breast cancer

May 1 2005

Exposure to carcinogens in traffic emissions at particular lifetime points may increase the risk of developing breast cancer in women who are lifetime nonsmokers, a study by epidemiologists and geographers at the University at Buffalo has found.

Their study was conducted among women who lived in Erie and Niagara counties of New York State between 1996 and 2001. They found that higher exposure around the time of first menstruation to polycyclic aromatic hydrocarbons (PAHs), potential carcinogens found in traffic emissions, was associated with increased risk of premenopausal breast cancer.

However, for postmenopausal women, higher exposure to PAHs at the time of the first birth was associated with increased risk. Neither association was found in women with a history of smoking.

Results of the study were presented earlier this month at the annual meeting of the American Association for Cancer Research held in Anaheim, Calif. Jing Nie, Ph.D., a postdoctoral fellow in epidemiology in UB's School of Public Health and Health Professions is first author on the study.

"There is growing evidence that there may be times in a woman's life when exposures to potential carcinogens may be critical for breast-cancer initiation and development," said Nie. "Our study findings support the hypothesis that exposures in early life contribute to breast-cancer risk."

The study was based on data from the Western New York Exposures and Breast Cancer (WEB) study. All participants were women between the ages of 35 and 79 who lived in Erie or Niagara counties at the time of data collection. Women with primary, histologically confirmed breast cancer served as cases. Controls were randomly selected and matched to cases on age, race and county of residence.

Researchers in the WEB study conducted in-depth personal interviews with study participants to collect data on potential breast-cancer risk factors and a history of where they had lived at different times in their lives. Researchers were interested particularly in information related to four time periods: menarche (first menstrual period), first birth, 20 years prior to the interview and 10 years prior.

Several information sources provided data on traffic volumes on roads in question for the years from 1960 to 2002 and tail-pipe emissions, including measurements from tunnels and tests on individual vehicles. A geographic model was used to reconstruct historic traffic PAHs, using measurements of benzo[a]pyrene, a known potent mutagen and carcinogen, as a surrogate for total PAH exposure. Cruise emissions, cold engine emissions and intersection emissions were used to estimate total traffic PAH emissions.

In addition, meteorological information was used in a geographic dispersion model to determine PAH exposure at each participant's residence.

While the researchers found increased risk for exposure at menarche and first birth for premenopausal and postmenopausal participants, respectively, who were lifetime nonsmokers, there was no association of traffic emissions with breast cancer for the other time periods.

Nie said these findings related to PAHs need to be interpreted with caution, because they could be explained by other compounds in vehicle exhaust or by other exposures related to the traffic emissions.

"While these results are subject to the limitations of epidemiologic observational studies, they are provocative in providing evidence both of the importance of early exposures and of the potential importance of an environmental agent in risk of breast cancer," said Nie. "Further examination of PAH exposure in early life is clearly warranted."

The UB researchers currently are examining whether genetic polymorphisms involving PAH metabolism may modify the risk, if lifeline cumulative exposure may be associated with the risk and if this study may be replicated in another geographic settings.

Jo Freudenheim, Ph.D., UB professor of social and preventive medicine, heads the WEB study.

Additional researchers were Jan Beyea, Ph.D., from Consulting in the Public Interest of Lambertville, N.J., who developed the geographic dispersion model; Matthew Bonner, Ph.D., of the National Cancer Institute (NCI); Daikwon Han, Ph.D., Dominica Vito, and Maurizio Trevisan, M.D., from the Department of Social and Preventive Medicine, UB School of Public Health and Health Professions; and Peter Rogerson, Ph.D., of the Department of Geography, UB College of Arts and Sciences, along with John Vena, Ph.D., now at the University of South Carolina, and Paola Muti, M.D., now at Italy's National Cancer Institute in Genoa.

The research was supported in part by grants from the U.S. Army Breast Cancer Research Program and NCI.

The University at Buffalo is a premier research-intensive public university, the largest and most comprehensive campus in the State University of New York.