Environment and Breast Cancer: Science Review

Evidence From Humans
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Health effects and exposure to polychlorinated biphenyls (PCBs) and metals in a contaminated community
Helmfrid, I., Berglund, M., Lofman, O., Wingren, G. Environ Int. 2012. 44, 53-8.
Topic area
Environmental pollutant - PCBs Metals
Study design
Population based case-control
Funding agency
Cancer and Allergy Fund, Sweden
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: 625
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
All cancer diagnoses, registered in 1960-2003 for living in the parish including the contaminated area, were collected from the regional cancer registries in southeast Sweden. Five controls per case were randomly selected from population registers available from Statistics Sweden for 1972-2002, and additional subjects were randomly chosen from 1972 to serve as controls for cases that occurred between 1960 and 1971, since identification was not available from the registers for those years. The controls were selected based on residency in the area during the same year the cases received the cancer diagnosis. Questionnaires were sent to all subjects, above 18 years of age, in 2005. Only subjects with a latency of at least 5 years between first time of residence in the contaminated area and year of cancer diagnosis, or year of inclusion for controls, were included in the analyses. Cancer incidence rates for the Swedish population for the same time period were collected from the National Cancer Register. The cancer cases and background population were stratified by gender, 5 year age groups, and calendar year of diagnosis.
Comment about participation selection
28% of cancer cases and 20% of controls returned the empty questionnaire with reasons why they did not want to participate; the most frequent explanation was that they were too sick. The responders may have been a healthier population, and some risk associations may have been underestimated.
Exposure Investigated
Exposures investigated
Self-reported consumption patterns of local food for the past 30 years, including fish, berries, mushrooms, garden vegetables. Occupation as farmer or metalworker engaged in zipper production was assessed.
How exposure was measured
Questionnaire, self-administered Job history
Exposure assessment comment
A 1972 oil spill contaminated the river that runs through the study area with PCBs. Consumption of fish was treated as a proxy for PCB exposure, due to previous measurements of high levels of PCBs in local fish. Work in metal production was considered a proxy for Zn, Cu and Pb exposure. Work in zipper production was considered a proxy for Cu, Zn, Ni, Ag, Cr, Sn exposure. These occupations may also have exposure to solvents and other chemicals. Consumption of fish was treated as a proxy for PCB exposure, due to previous measurements of high levels of PCBs in fish.
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, smoking
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
Register-based study:
Living in study area SIR 0.97 (95% CI 0.77-1.21)

Questionnaire-based study:
Ate local perch >2x/month (2 cases) OR 7.90 (95% CI 1.01-61.9)
Ate local pike >2x/month (2 cases) OR 9.07 (95% CI 1.10-74.4)
Ever work in metal production (6 cases) OR 3.99 (95% CI 1.13-14.1)
Ever work in zipper production (3 cases) OR 4.36 (95% CI 0.85-22.3)
Results Comments
The number of exposed cases and controls was small, having limited statistical power.
Author address
Occupational and Environmental Medicine, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linkoping University, Linkoping, Sweden. ingela.helmfrid@lio.se
Reviewers Comments
The 1972 oil spill provides researchers with an opportunity to investigate the impact of exposure in discrete time periods.