Environment and Breast Cancer: Science Review

Evidence From Humans
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Breast cancer risk after occupational solvent exposure: the influence of timing and setting
Ekenga, C. C., Parks, C. G., D'Aloisio, A. A., DeRoo, L. A., Sandler, D. P. Cancer Res. 2014. 74:11, 3076-83.
Topic area
Environmental pollutant - Occupation Organic solvents
Study design
Prospective cohort
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
No analyses based on menopausal status
Number in Cohort
Cohort: 47,661
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 and never exposed to solvents, degreasers or cleaning agents were the study's reference group.
Exposures investigated
Self-reported occupational exposure to "solvents, degreasers or cleaning agents" collected at baseline interview
How exposure was measured
Job history Occupational exposures, self-reported
Early life exposures considered
Yes, before first childbirth
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, 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
Total duration of solvent job(s) exposure among all women:
1 to < 5 years: HR 0.98 (95% CI 0.74-1.32)
5 to < 10 years: HR 0.96 (95% CI 0.68-1.35)
10+ years HR: 1.14 (95% CI 0.90-1.45)

Among parous women, duration of solvent job exposure relative to first birth:
5+ years before first birth: HR 1.42 (95% CI 0.92-2.20)
3 to <5 years before first birth: HR 1.30 (95% CI 0.80-2.10)
<3 years before first birth: HR 0.92 (95% CI 0.57-1.49)
After first birth: HR 0.97 (95% CI 0.75-1.25)
Trend: p=0.04

Among women with ER+ tumors compared to women who never had a solvent job:
Held solvent job before 1980: HR 1.28 (95% CI 1.01-1.62)
Held solvent job before first birth: HR 1.39 (95% CI 1.03-1.86)
Results Comments
There was also a marginally significant trend for duration of solvent work before first childbirth and ER+ tumors (p-trend =0.05), but not for ER- tumors. No association between frequency of exposure (<1/wk and ≥1/wk compared to never) and breast cancer.
Author address
Authors' Affiliations: Epidemiology Branch, National Institute of Environmental Health Sciences, NIH, Department of Health and Human Services, Research Triangle Park, North Carolina; and Department of Global Public Health and Primary Care, University of B