A new study has reported that both the long-term time trend and geographic pattern of motor vehicle emissions are associated with breast cancer rates. Motor vehicles are the primary source of nitrogen dioxide (NOx) emissions, so that NOx is a convenient marker for motor vehicle-derived air pollution. Breast cancer rates in the U.S. and some European countries have followed a similar long-term pattern of increasing incidence in the 20th century, followed by a declining trend in the current century. Established breast cancer risk factors cannot explain this pattern. To conduct the study, the authors compared breast cancer trends based on Surveillance, Epidemiology, and End Results (SEER) data with NOx emission and monitoring data, as well as motor vehicle density data.

The pattern of an upward trend followed by a downward trend was also found for NOx. However, the NOx curve started 20 years earlier, which is consistent with possibility that automobile emissions are a risk factor for breast cancer. The authors conducted an analysis that showed that the geographic distribution of motor vehicle density in 1970 in selected U.S. counties appeared to be linked to breast cancer incidence rates in those counties during 1980 to 1995. The authors conclude that further studies concerning the relationship between breast cancer and air pollution are needed.

Living close to roadways could increase breast cancer risk

The study adds to a trickle of data suggesting that vehicle-derived air pollution might increase the risk of breast cancer. At this point, it is not clear which fractions of vehicle exhaust are responsible for any such increased risk. The results re-enforce the idea that living close to freeways or other roadways with heavy traffic can damage health.