Environment and Breast Cancer: Science Review

Evidence From Humans
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Risk of breast cancer for women living in rural areas from adult exposure to atrazine from well water in Wisconsin
McElroy, J. A., Gangnon, R. E., Newcomb, P. A., Kanarek, M. S., Anderson, H. A., Brook, J. V., Trentham-Dietz, A., Remington, P. L. J Expo Sci Environ Epidemiol. 2007. 17:2, 207-14.
Topic area
Environmental pollutant - Pesticides Drinking Water
Study design
Population based case-control
Funding agency
Not reported
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
No analysis based on menopausal status
Number of Controls
Controls: 3,669
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Cases were women between the ages of 20 and 79 years, with incident invasive breast cancer, identified from the Wisconsin Statewide Tumor Registry between 1988 and 2001. Controls with no history of breast cancer were selected randomly from the Wisconsin population, using lists from the Department of Transportation (age 20-64) and US Health Care Financing Administration (age 65-79) with matching to obtain similar age distributions. Analyses were limited to women who lived in rural areas of Wisconsin that did not have a public water system, restricted from the original study of over 10,000 cases and 10,000 controls. Women with interviews considered unreliable by interviewers were excluded (7 cases and 8 controls).
Comment about participation selection
High participation rates for such a large population-based study. Use of phone-interviews and no biological samples may have reduced selection bias in the rural population.
Exposure Investigated
Exposures investigated
Average atrazine exposure level (ppb) modeled at participant's home address at index date based on three well water sampling campaigns conducted by Wisconsin Department of Agriculture in 1994, 1996, and 2001.
How exposure was measured
Environmental sample GIS/geographic location Other: Environmental model
Exposure assessment comment
Atrazine exposure modeling utilized a unique dataset available from the Wisconsin State Department of Agriculture, based on sampling conducted at three different time points, starting in 1994. Modeling exposure based on measurements starting in 1994 while looking at incident breast cancer cases beginning in 1988 assumes prior atrazine exposure to be correlated with concentrations from 1994 on. There is some concern about potential misclassification of exposure given lack of tap water samples, lack of residential history and variation in atrazine levels in ground water with depth.
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.
Age at diagnosis, parity, age at first pregnancy, menopausal status, age at menopause, age at menarche, physical activity, recent alcohol consumption, family history of breast cancer, BMI, and education.
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
State of Wisconsin (rural areas):
0.15-0.50 ppb vs. <0.15 ppb: aOR 1.0 (95%CI 0.9 to 1.2)
0.51-1.00 ppb vs. <0.15 ppb: aOR 1.0 (95% CI 0.8-1.2)
1.01-2.99 ppb vs. <0.15 ppb: aOR 1.1 (95% CI 0.9-1.4)
≥3.0 ppb vs. <0.15 ppb: aOR 1.3 (95% CI 0.3-5.0)

Sub-analysis of high atrazine use counties (rural areas):
0.15-0.50 ppb vs. <0.15 ppb: aOR 1.1 (95% CI 0.7-1.5)
0.51-1.00 ppb vs. <0.15 ppb: aOR 0.9 (95% CI 0.6-1.3)
1.01-2.99 ppb vs. <0.15 ppb: aOR 0.9 (95% CI 0.6-1.4)
≥3.0 ppb vs. <0.15 ppb: aOR 1.2 (95% CI 0.3-5.8)
Results Comments
Only nine women (4 cases & 5 controls) in the high exposed group (≥ 3.0 ppb, which is the EPA maximum contaminant level)
Author address
University of Wisconsin Comprehensive Cancer Center, Madison, WI 53726, USA. jamcelroy@wisc.edu
Reviewers Comments
The atrazine exposure model may not accurately capture a woman's actual or historical exposure to atrazine; for example, other water sources outside of the home were not accounted for. Mean age at diagnosis in this population was 56 years, younger than the average age at breast cancer diagnosis, so additional follow-up is needed.