Environment and Breast Cancer: Science Review

Evidence From Humans
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Update: cohort mortality study of workers highly exposed to polychlorinated biphenyls (PCBs) during the manufacture of electrical capacitors, 1940-1998
Prince, M. M., Hein, M. J., Ruder, A. M., Waters, M. A., Laber, P. A., Whelan, E. A. Environ Health. 2006. 5, 13.
Topic area
Environmental pollutant - PCBs Occupation
Study design
Follow-up of retrospective cohort
Funding agency
Not reported
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
No analysis based on menopausal status
Number in Cohort
Cohort: 1,325 women
Cohort participation rate
Not applicable. This study was records-based.
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
This National Institute for Occupational Safety and Health (NIOSH) cohort consisted of workers employed at least 90 days in electrical capacitor manufacturing at a New York plant between 1946-1977 or at a Massachusetts plant between 1939-1976. This analysis was limited to 2,572 workers (1,325 women) identified as having highest/most direct PCB exposure. Workers determined to have solvent exposure at study start were excluded. Mortality was followed through 1998 using records from SSA, IRS, NDI, US postal service and credit bureaus. Cause of death identified from NDI plus and death certificates with review by nosologist. NDI does not include deaths before 1979, so workers lost to follow-up before that year were censored at date last observed.
Comment about participation selection
This occupational cohort uniquely looks at workers exposed to PCBs >20 years ago, allowing for a latency period that is consistent with that of breast cancer.
Exposure Investigated
Exposures investigated
Ever employed for ≥90 days in one of the two electrical capacitor manufacturing plants in a job task with high and direct exposure to PCBs. Duration of employment also considered.
Exposure assessment comment
The exposure experienced by these workers resulted from jobs such as impregnation, sealing, and testing of capacitors. Air sampling conducted by NIOSH in 1977 found higher air concentrations of PCBs in MA plant than NY Plant. However, neither individual measures on cohort members nor historical environmental sampling measures were used in the exposure assessment. The following commercialPCB mixtures were used at both plants: Aroclor 1254 (54% chlorine, phased out in 1950s at plant 1), Aroclor 1242 (42% chlorine, first used at plant 1 in 1971), and Aroclor 1016 (41% chlorine). There was likely overlap between the types of Aroclor used at a particular time, and less chlorinated versions were used in more recent years. No information available about dates of use at plant 2.
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, calendar time
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
Breast cancer mortality among capacitor cohort compared to US breast cancer mortality rate:

Overall: SMR 0.59 (95% CI 0.33-0.98)

Duration of employment:
<5 years (5 cases): SMR 0.61 (95% CI 0.20-1.43)
5-9 years (2 cases): SMR 0.39 (95% CI 0.05-1.40)
≥10 years (8 cases): SMR 0.67 (95% CI 0.29-1.32)
Results Comments
Compared to previous analyses of this cohort, this analysis excluded 16 workers found to have been employed < 90 days and corrected gender information for 34 workers. Authors considered race to some extent in analysis, but note that race was not recorded in company records for plant 2 and anyone with unknown race was assumed to be white. The authors considered using surrounding counties' breast cancer rates for comparison, but state that this did not change the results (data not shown).
Author address
Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Division of Surveillance, Hazard Evaluation and Field Studies, Industrywide Studies Branch, Cincinnati, Ohio 45226, USA. mmprince12@earthlink.net
Reviewers Comments
Mortality is not a sensitive measure of breast cancer risk. Because the general population was chosen as the comparison population, effect estimates may be biased downward due to the healthy worker effect (HWE). However, SMR for all deaths did not show evidence of HWE (among women, SMR for all deaths = 1.00; 95%CI: 0.91-1.09).