Environment and Breast Cancer: Science Review

Evidence From Humans
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Hazardous air pollutants and breast cancer risk in California teachers: a cohort study
Garcia, E., Hurley, S., Nelson, D. O., Hertz, A., Reynolds, P. Environ Health. 2015. 14:1, 14.
Topic area
Environmental pollutant - Air pollution
Study design
Prospective cohort
Funding agency
Department of Defense NCI California Breast Cancer
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Analyses stratified based on menopausal status
Number in Cohort
Cohort: 112,378
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
The study population was enrolled in the California Teachers Study in 1995-1996. Of these 133,479 active and retired teachers, those who were not residing in California at baseline, had an unknown history of prior cancer, had a prior history of invasive or in situ breast cancer, asked to be removed from the study, or had an address that could not be geocoded were excluded. The total eligible population was 112,378 women who were followed until 2011 through the California Cancer Registry. Median age at enrollment was 54.
Exposure Investigated
Exposures investigated
Census tract-level modeled ambient concentrations of 24 hazardous air pollutants (HAPs) from 2002 National-Scale Air Toxics Assessment (NATA) used to estimate exposure at baseline address. NATA estimates are produced by US EPA using emissions data. The 24
How exposure was measured
GIS/geographic location EPA National-Scale Air Toxics Assessment (2002)
Exposure assessment comment
Exposures were classified into quintiles based on concentrations of individual chemicals and a summary measure of all chemicals. The air pollutant data was taken from 2002, which was mid-way through the study's follow-up period. The use of the single-year data does not capture changes in air pollution concentrations over time. Since the concentrations were also modeled on a census-wide basis, they do not account for intra-census variation.
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, race/ethnicity, family history, age at menarche, age at first child birth, total lifetime breastfeeding months, menopausal status and hormone therapy use at baseline, physical activity, BMI, alcohol consumption, smoking status, and total pack-years o
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
Among all women:
acrylamide, 5th quintile vs. 1st quintile: HR 1.08 (95% CI 1.01-1.16)
benzene, 5th quintile vs. 1st quintile: HR 1.06 (95% CI 0.98-1.16)

ER+/PR+ tumors:
carbon tetrachloride, 5th quintile vs. 1st quintile: HR 1.13 (95% CI 1.03-1.25)
benzidine, 5th quintile vs. 1st quintile: HR 1.12 (95% CI 1.03-1.20)
acrylamide, 5th quintile vs. 1st quintile: HR 1.04 (95% CI 0.98-1.16)

ER-/PR- tumors:
benzene, 5th quintile vs. 1st quintile: HR 1.45 (95% CI 1.15-1.83)

Among pre/perimenopausal women:
propylene oxide, 3rd quintile vs. 1st quintile: aHR 1.23 (95% CI 1.05-1.44)

Among postmenopausal women:
carbon tetrachloride, 5th quintile vs. 1st quintile: aHR 1.13 (95% CI 1.02-1.26)
vinyl chloride, 3rd quintile vs. 1st quintile: aHR 1.14 (95% CI 1.02-1.26)
Results Comments
Analyses were stratified by smoking status for 18 MGCs with tobacco smoke as a potential source; results were not show but described as generally similar. Some MGCs (e.g. ethylene dichloride and vinyl chloride) had somewhat stronger ORs for Q5 vs Q1 among women who were not currently using hormone therapy (past or never users). OR for benzene and ER-/PR- tumors remained significant after adjustment for multiple comparisons.
Reviewers Comments
A strength of the study is that the exposures come from a list of mammary gland carcinogens.