breast cancer caused by air pollution?!

I found an article entitled "Breast Cancer Possibly Linked to Air Pollution" by Michael Graham Richard on TreeHugger's blog. http://www.treehugger.com/files/2010/10/breast-cancer-possibly-linked-to-air-pollution-study.php?campaign=th_rss There was a study done in 1996-97 in Canada where scientists tracked nitrogen dioxide in the air, and the addresses of where women with breast cancer were living. Across Montreal levels of NO2 were between 5 parts per billion and 30 parts per billion.  The scientists discovered that the risk of breast cancer increased 25% with every 5 ppb.  This means that that women living in the more polluted areas were almost twice as likely to develope breast cancer then the women living in the less polluted areas!  They are not saying that NO2 causes breast cancer but they are looking at it as a possible contributing cause and more research will need to be done before any conclusions are made.
In class, we have talked about pollution and how it effects people and the environment, and this article is a great example of that.  I would have never expected pollution to have this kind of effect on people!  I know that Pennsylvania has a high pollution rate, although i'm not sure about the nitrogen dioxide levels in the air, but this still worries me. I hope that there are ways to cut back on the NO2 pollution so we can help save women's lives, if this really is contributing to breast cancer of course.