Environment and Breast Cancer: Science Review

Evidence From Humans
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Spatial variations in the incidence of breast cancer and potential risks associated with soil dioxin contamination in Midland, Saginaw, and Bay Counties, Michigan, USA
Dai, D., Oyana, T. J. Environ Health. 2008. 7, 49.
Topic area
Environmental pollutant - TCDD Dioxin
Study design
Funding agency
Graduate School of Southern Illinois University, C
Study Participants
Number of Cases
22 zip codes with 4,604 cases
Menopausal Status
The menopausal status of women included in this study is listed here.
No analyses by menopausal status
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Breast cancer cases were women >14 years old, diagnosed between 1985 and 2002, identified in the state-wide cancer registry, living in 22 zip codes in 3 Michigan counties with dioxin contamination..
Comment about participation selection
One zip code (48883) was chosen as the referent geographical population because its levels of dioxin were close to background levels across other parts of Michigan, with the assumption that this population was unexposed.
Exposure Investigated
Exposures investigated
Soil dioxin concentrations were modeled using environmental sampling data by zip code of residence.
How exposure was measured
Environmental sample GIS/geographic location
Exposure assessment comment
The exposure assessment was based on soil sampling conducted between 1995 and 2003 at varying levels of depth below the surface. Parts of the Tittabawassee River flood annually, to varying extents, and it is possible that flooding patterns may contribute to sweeping and redepositing dioxin-contaminated soil across the floodplain which may contribute to exposure misclassification.
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.
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
After adjustment for multiple comparisons:
zip code 48640 (Midland) vs. zip code 48883: aOR 1.86 (95% CI 0.32-0.92)
zip code 48880 (Tittabawassee and Saginaw River) vs. zip code 48883: aOR 1.88 (95% CI 0.27-0.98)

The exposure assessment for dioxin levels in soil shows that the city of Midland and the floodplain of the Tittabawassee River were highly contaminated. The reference area (48883) was upstream of dioxin contamination.
Author address
Environmental Resources and Policy Program, Southern Illinois University, 405 West Grand Avenue, MC 4637, Carbondale, IL 62901-4637, USA. ddai@niu.edu
Reviewers Comments
A limitation of the ecologic study design is the lack of individual risk factor information.