Provocative new Montreal study probes link between breast cancer and air pollution
Air pollution has already been linked to a range of health
problems. Now, a ground-breaking new study suggests pollution from
traffic may put women at risk for another deadly disease. The
study, published in the prestigious journal Environmental Health
Perspectives, by researchers from The Research Institute of the
MUHC (RI MUHC; Dr. Mark Goldberg), Âé¶čAV (Drs.
Goldberg, Dan Crouse and Nancy Ross), and Université de Montréal
(Dr. France LabrĂšche), links the risk of breast cancer â the
second leading cause of death from cancer in women â to
traffic-related air pollution.
âWeâve been watching breast cancer rates go up for some time, âsays
study co-author Dr. Mark Goldberg, a researcher at The RI MUHC.
âNobody 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.â
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 âmapsâ showing levels
of nitrogen dioxide (NO2), a by-product of vehicular traffic, in
different parts of the city 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.
âWe found a link between post-menopausal breast cancer and exposure
to nitrogen dioxide (NO2), which is a âmarkerâ for traffic-related
air pollutionâ, says Dr. Goldberg. âAcross 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.â
These disturbing results must be interpreted with great caution,
warns Dr. Goldberg. âFirst of all, this doesnât mean NO2
causes breast cancer,â he explains. âThis 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 â some of which are known carcinogens. NO2 is only a
marker, not the actual carcinogenic agent.â
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. âFor example, we donât 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,â says Dr. Goldberg.
Dr. LabrĂšche adds âSome 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 aiming at a
reduction of traffic-related air pollution in residential
areas.â