Breast cancer is one of the most prevalent cancers found in women, but known risk factors only account for about half of all diagnosed cases. Scientists have been trying to determine with greater certainty what risk factors there are in order to close this knowledge gap. A pair of recent studies looked at the relationship between air pollution and breast cancer.
Air pollution is a known factor in causing lung cancer, though it is not as significant of a factor as cigarette smoking is. Because of its role as a known carcinogen and because rates of breast cancer are higher in more developed countries than in less developed countries, scientists have been investigating the role of air pollution (something that developed countries have more of) in breast cancer rates. Starting with this hypothesis, both groups of scientists looked at large samples of women and found as many as they could where there was good data on both their history with cancer and their exposure to air pollution. They then began the hard work of crunching numbers and defining “air pollution.”
One problem with looking at air pollution as a cause of cancer is that air pollution is essentially just a catchall term for a vast array of chemicals and particles that can be suspended in our atmosphere. The other problem is that “cancer” is not a single disease; there are many types of breast cancer, which can be caused by different things. The scientists were not simply trying to see if some kinds of air pollution could cause breast cancer, but also what kinds of pollution could cause which kinds of cancer. One of the two studies (Here) looked at fine particulates and nitrogen dioxide, while the other (Here) focused on a variety of organic molecules and petroleum-based chemicals. While neither study found a strong correlation between air pollution and breast cancer generally, both did find that there seemed to be a correlation between some certain pollutants and the ER+/PR+ types of breast cancer. Specifically, nitrogen dioxide, propylene oxide, and vinyl chloride were all found to be associated with a small but noticeably increased risk of ER+/PR+ breast cancer tumors. These are known as the hormone receptor positive cancers, which make up about 60% of invasive breast cancers.
Neither of these studies was definitive, but both produced useful results which merit further investigation. As is often the case with complex issues, it is best not to make too much of any single study or experiment. In this case, it is safe to say that air pollution certainly has harmful health effects, but is not clearly linked to breast cancer specifically. The links between ER+/PR+ cancer and the three identified chemicals are not conclusive, but warrant additional study to determine if a clear causal relationship exists.