Environment and Breast Cancer: Science Review

Evidence From Humans
Print this page
Postmenopausal breast cancer is associated with exposure to traffic-related air pollution in Montreal, Canada: a case-control study
Crouse, D. L., Goldberg, M. S., Ross, N. A., Chen, H., Labreche, F. Environ Health Perspect. 2010. 118:11, 1578-83.
Topic area
Environmental pollutant - Air pollution Vehicle exhaust
Study design
Hospital based case-control
Funding agency
Canadian Institutes for Health Research Canadian B
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
All women in the study were postmenopausal
Number of Controls
Controls: 416
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
The study population consisted of postmenopausal women, 50-75 years of age at time of diagnosis, who in 1996 and 1997 were residents of the Island of Montreal and Nun's Island. Cases had primary, histologically confirmed, invasive breast cancer, and they were identified through 18 hospitals in the region that treated breast cancer. Controls were matched to cases by hospital and age, and they had 1 of 32 other selected sites of incident, histologically confirmed cancers. Liver, intrahepatic bile duct, pancreas, lung, bronchus and trachea, brain and central nervous system, leukemias and lymphomas were excluded because of their possible association with occupational exposures.
Comment about participation selection
The study aimed to minimize the potential for recall bias by including controls with cancers, who were matched to the same hospital as the cases. The study also attempted to control for confounding by occupational exposures by excluding cancers with a possible association to occupational exposures.
Exposures investigated
Ambient NO2 measurements from 13 measurement stations in Montreal, extrapolated to the 10 year period between 1985 and 1996 (approximately 10 year period before diagnosis).
How exposure was measured
Environmental sample Questionnaire, self-administered Geographic location
Breast cancer outcome investigated
Primary incident breast cancer
Confounders considered
Other breast cancer risk factors, such as family history, age at first birth, and hormone replacement therapy use, that were taken into account in the study.
Hospital of diagnosis, mother or sister with breast cancer, oophorectomy, years of education, ethnicity, age at menarche, age at first full-term pregnancy, breast-feeding history, oral contraceptive use, hormone replacement therapy use, body mass index, e
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked “Yes.” “No”, if not.
Strength of associations reported
Per 5 ppb increase in NO2:
1996: aOR 1.36 (95% CI 0.99-1.88)
1985: aOR 1.17 (95% CI 0.91-1.50)
Mean of 1996 and 1985: aOR 1.25 (95% CI 0.94-1.65)

Per 5 ppb increase in NO2, limited to participants at same address at least 10 years before interview
1996: aOR 1.42 (95% CI 0.81-2.48)
1985: aOR 1.28 (95% CI 0.84-1.93)
Mean of 1996 and 1985: aOR 1.34 (95% CI 0.83-2.16)
Results Comments
ORs from analyses using alternative extrapolated NO2 surfaces based on predicted (rather than observed) NO2 from the 2006 LUR levels were similar.
BACKGROUND: Only about 30% of cases of breast cancer can be explained by accepted risk factors. Occupational studies have shown associations between the incidence of breast cancer and exposure to contaminants that are found in ambient air. OBJECTIVES: We sought to determine whether the incidence of postmenopausal breast cancer is associated with exposure to urban air pollution. METHODS: We used data from a case-control study conducted in Montreal, Quebec, in 1996-1997. Cases were 383 women with incident invasive breast cancer, and controls were 416 women with other incident, malignant cancers, excluding those potentially associated with selected occupational exposures. Concentrations of nitrogen dioxide (NO2) were measured across Montreal in 2005-2006. We developed a land-use regression model to predict concentrations of NO2 across Montreal for 2006, and developed two methods to extrapolate the estimates to 1985 and 1996. We linked these estimates to addresses of residences of subjects at time of interview. We used unconditional logistic regression to adjust for accepted and suspected risk factors and occupational exposures. RESULTS: For each increase of 5 ppb NO2 estimated in 1996, the adjusted odds ratio was 1.31 (95% confidence interval, 1.00-1.71). Although the size of effect varied somewhat across periods, we found an increased risk of approximately 25% for every increase of 5 ppb in exposure. CONCLUSIONS: We found evidence of an association between the incidence of postmenopausal breast cancer and exposure to ambient concentrations of NO2. Further studies are needed to confirm whether NO2 or other components of traffic-related pollution are indeed associated with increased risks.
Author address
Department of Geography, McGill University, Montreal, Quebec, Canada. daniel.crouse@mail.mcgill.ca