This release is available in French.
The study, published in the prestigious journal Environmental Health Perspectives, by researchers from The Research Institute of the MUHC (RI MUHC; Dr. Mark Goldberg), McGill University (Drs. Goldberg, Dan Crouse and Nancy Ross), and Université de Montréal (Dr. France Labrèche), links the risk of breast cancer – the second leading cause of death from cancer in women – to traffic-related air pollution.
“We’ve been watching breast cancer rates go up for some time, “says study co-author Dr. Mark Goldberg, a researcher at The RI MUHC. “Nobody really knows why, and only about one third of cases are attributable to known risk factors. Since no-one had studied the connection between air pollution and breast cancer using detailed air pollution maps, we decided to investigate it.”
Dr. Goldberg and his colleagues approached the problem by combining data from several studies. First, they used the results of their 2005-2006 study to create two air pollution “maps” showing levels of nitrogen dioxide (NO2), a by-product of vehicular traffic, in different parts of Montreal in 1996 and 10 years earlier in 1986.
Then, they charted the home addresses of women diagnosed with breast cancer in a 1996-97 study onto the air pollution maps. Their findings were startling. The incidence of breast cancer was clearly higher in areas with higher levels of air pollution.
“We found a link between post-menopausal breast cancer and exposure to nitrogen dioxide (NO2), which is a ‘marker’ for traffic-related air pollution”, says Dr. Goldberg. “Across Montreal, levels of NO2 varied between 5 ppb to over 30 ppb. We found that risk increased by about 25 per cent with every increase of NO2 of five parts per billion. Another way of saying this is that women living in the areas with the highest levels of pollution were almost twice as likely to develop breast cancer as those living in the least polluted areas.”
These disturbing results must be interpreted with great caution, warns Dr. Goldberg. “First of all, this doesn’t mean NO2 causes breast cancer,” he explains. “This gas is not the only pollutant created by cars and trucks, but where it is present, so are the other gases, particles and compounds we associate with traffic – some of which are known carcinogens. NO2 is only a marker, not the actual carcinogenic agent.”
A study of this kind can be subject to unknown errors. While the researchers tried to account as much as possible for them, areas of uncertainty remain. “For example, we don’t know how much the women in the study were exposed to pollution while at home or at work, because that would depend on their daily patterns of activity, how much time they spend outdoors and so on,” says Dr. Goldberg.
Dr. Labrèche adds “Some studies published in the US have also shown possible links between cancer and air pollution. At the moment, we are not in a position to say with assurance that air pollution causes breast cancer. However, we can say that the possible link merits serious investigation. From a public health standpoint, this possible link also argues for actions aimed at reducing traffic-related air pollution in residential areas.”
About the study
The study was a collaborative effort by researchers from the Research Institute of the MUHC, McGill University and Université de Montreal. It was funded by a research grant from the Canadian Cancer Society and another one from the Canadian Institutes of Health Research (CIHR).
About the McGill University Health Centre (MUHC) One of the world’s foremost academic health centres, the MUHC offers exceptional and integrated patient-centric care, research and teaching. Highly committed to the continuum of care in its community and affiliated with the Faculty of Medicine of McGill University, The Montreal Children’s Hospital, the Montreal General Hospital, the Royal Victoria Hospital, the Montreal Neurological Hospital, the Montreal Chest Institute and the Lachine Hospital of the MUHC value multidisciplinary service throughout the lifespan, innovative technologies and practices, strategic partnerships and leadership in knowledge transfer. The MUHC is currently carrying out a $2.25-billion Redevelopment Project on three campuses—the Mountain, the Glen and Lachine—designed to provide healthcare professionals with an effective environment in which to ensure patients and their families benefit from The Best Care for Life. The campuses are also anchored in best sustainable-development practices, including LEED® and BOMA BESt guidelines. www.muhc.ca www.muhc.ca/construction
The Research Institute of the McGill University Health Centre (RI MUHC) is a world-renowned biomedical and health-care hospital research centre. Research is organized by eleven research axes (or programs). Located in Montreal, Quebec, Canada, the Institute is the research arm of the McGill University Health Centre affiliated with the Faculty of Medicine at McGill University. The Institute supports over 600 researchers, 1,000 graduate students, post-docs and fellows devoted to a broad spectrum of fundamental and clinical research. Over 1000 clinical research studies are conducted within our hospitals each year. The Research Institute of the MUHC is supported in part by the Fonds de la recherche en santé du Québec (FRSQ). www.muhc.ca/research/
About McGill University
McGill University, founded in Montreal, Que., in 1821, is Canada’s leading post-secondary institution. It has two campuses, 11 faculties, 10 professional schools, 300 programs of study and more than 35,000 students. McGill attracts students from more than 150 countries around the world. Almost half of McGill students claim a first language other than English – including 6,200 francophones – with more than 6,800 international students making up almost 20 per cent of the student body. www.mcgill.ca
About the Université de Montréal
Deeply rooted in Montreal and dedicated to its international mission, the Université de Montréal is one of the top universities in the French-speaking world. Founded in 1878, the Université de Montréal today has 16 faculties and together with its two affiliated schools, HEC Montréal and École Polytechnique, constitutes the largest centre of higher education and research in Québec, the second largest in Canada, and one of the major centres in North America. It brings together 2,500 professors and researchers, accommodates more than 56,000 students, offers some 650 programs at all academic levels, and awards about 3,000 masters and doctorate diplomas each year. www.umontreal.ca