Environment and Breast Cancer: Science Review

Evidence From Humans
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Occupation and breast cancer: a Canadian case-control study
Brophy, J. T., Keith, M. M., Gorey, K. M., Luginaah, I., Laukkanen, E., Hellyer, D., Reinhartz, A., Watterson, A., Abu-Zahra, H., Maticka-Tyndale, E., Schneider, K., Beck, M., Gilbertson, M. Ann N Y Acad Sci. 2006. 1076, 765-77.
Topic area
Environmental pollutant - Occupation
Study design
Population based case-control
Funding agency
Workplace Safety and Insurance Board Research Advi
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: 599
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Cases were women diagnosed with pathologically confirmed breast cancer, recruited from a regional cancer center. Community controls were chosen at random using city directory software, matched by age and by geographical area.
Comment about participation selection
Cases and controls were both recruited by a letter and a telephone call.
Exposure Investigated
Exposures investigated
Self-reported occupational history with questions about a range of occupational exposures including asbestos, mineral fibers, dusts, second-hand tobacco smoke, engine exhaust, metal-working fluids, solvents, paints, strippers, pesticides, and chemicals. J
How exposure was measured
Questionnaire, in person
Exposure assessment comment
Self-reported occupational history by job title may or may not accurately reflect duration or intensity of any specific occupational exposure. One challenge in this study was how to accurately classify exposures for a wide variety of occupations. Because participants' recall regarding specific agents proved to be limited, exposure to specific agents was not included in the analysis.
Early life exposures considered
Though authors report that agricultural jobs were often among the first worked during adolescence, there were no specific analyses on early life exposures.
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, education, household income, BMI, number of pregnancies, oral contraceptive use, duration of breastfeeding, cigarette smoking, alcohol use, and marital status.
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
Based on history of employment in agriculture, automotive-related manufacturing, or health care:
Ever worked in agriculture: aOR 2.8 (95% CI 1.6-4.8)
Worked in agriculture and then in automotive-related manufacturing: aOR 4.1 (95% CI 1.7-9.9)
Worked in agriculture and then in health care: aOR 2.3 (95% CI 1.1-4.6)
Worked in automotive-related manufacturing (but never agriculture): aOR 0.76 (95% CI 0.59-1.10)
Worked in health care (but never agriculture): aOR 0.85 (95% CI 0.62-1.17)
Ever worked in retail: aOR 1.0 (95% CI 1.0-1.05)
Results Comments
The authors report that agricultural jobs tended to be among the first worked, often during adolescence. Subsequent study with a different population that considered previous work in agriculture didn't observe the interaction seen in this study (Brophy 2012). This study considered many additional job titles. We focus on (1) significant positive associations (2) if a particular job or sector was significantly associated with breast cancer in at least one study, we report results from all other studies that considered that sector, regardless of significance. It is important to note that job coding criteria generally differed across studies.
Author address
Occupational Health Clinics for Ontario Workers, Toronto, Ontario, Canada. jbrophy@ohcow.on.ca
Reviewers Comments
The exposure category of "ever farming" groups together many women who may have had different exposures in the agricultural setting; they differ, for example in duration, intensity, and chemical composition of the exposure. Because agricultural jobs were commonly worked during adolescence, the authors suggest that timing of agricultural exposure may influence risk.