Environment and Breast Cancer: Science Review

Evidence From Humans
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Chemical exposures in the workplace and breast cancer risk: A prospective cohort study
Ekenga, C. C., Parks, C. G., Sandler, D. P. Int J Cancer. 2015. .
Topic area
Environmental pollutant - Occupational exposures Organic solvents
Study design
Prospective cohort
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Stratified analysis based on menopausal status
Number in Cohort
Cohort: 45,640
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Women were enrolled as part of the Sister Study, a prospective cohort study of 50,884 women initially free of breast cancer, with sisters who had been diagnosed with breast cancer, enrolled between 2003 and 2009, and followed for an average of 4.7 years. Women were excluded from this study if they had incomplete occupational data, had no occupational history, or had been diagnosed with breast cancer before the baseline interview.
Comment about participation selection
Sister Study participants who were ever employed never exposed to solvents, degreasers or cleaning agents were the study's reference group. As the authors explain, because the Sister Study consists of women who had a sister with breast cancer, the results may not be generalizable to women without a family history of breast cancer.
Exposure Investigated
Exposures investigated
Self-reported occupational exposure to acids, dyes/inks, gasoline or other petroleum products, glues or adhesives, lubricating oils, metals, paints, pesticides, soldering materials, solvents, stains at baseline.
How exposure was measured
Questionnaire, by telephone
Exposure assessment comment
Cumulative exposure to each agent was estimated as a function of frequency and duration of use based on participant-reported data. Exposure levels were defined categorically (four quartiles and a "never use" referent category) as well as dichotomously (ever use or never use).
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.
Based on causal diagram: Race/ethnicity, education, income, parity, and age at first birth
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
Ever vs never exposed to solvents (invasive cases):
Q1 HR: 1.1 (95% CI 0.7-1.8)
Q2 HR: 0.9 (95% CI 0.5-1.5)
Q3 HR: 1.3 (95% CI 0.9-2.1)
Q4 HR: 0.9 (95% CI 0.5-1.5)

Premenopausal, invasive and in situ:
Solvents (ever vs. never) HR: 1.3 (95% CI 0.9-1.9)
Soldering materials (ever vs. never) HR: 1.8 (95% CI 1.1-3.0)
Results Comments
HRs were slightly non-significantly elevated among HR+ and HR- tumors with ever exposure to solvents.
Author address
Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC.
Reviewers Comments
The authors note that small number of exposed cases (e.g. 4 cases with high exposure to stains, 7 cases with high exposure to pesticide) limits analyses for those exposures. The difference in OR when Q4 of gasoline or petroleum product exposure is compared to those never exposed versus Q1 may indicate uncontrolled confounding in the comparison to women never occupationally exposed to solvents.