Environment and Breast Cancer: Science Review

Evidence From Humans
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Cancer incidence among large cohort of female Danish registered nurses
Kjaer, T. K., Hansen, J. Scandinavian journal of work, environment & health. 2009. 35:6, 446-53.
Topic area
Environmental pollutant - Occupation
Study design
Retrospective cohort
Funding agency
Danish Nurses' Association Danish Cancer Society
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: 90,822
Cohort participation rate
Not applicable, this is a records based study
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
The study population includes women with Danish nursing accreditation who were members of the Danish Nurses’ Association between April 1980-2001. Cases reported between April 1980 and December 2013 were collected from the nationwide Danish Cancer Registry. The external comparison population included a random sample of 91,878 women from Danish Central Population Register who were ever employed (per pension fund) in any field other than as a registered nurse, frequency-matched to nurses by year of birth.
Exposure Investigated
Exposures investigated
Employment history of all nurses who were members of the Danish Nurses' Association between 1980-2001 determined through linkage to the nationwide pension fund.
Exposure assessment comment
History of employment for each nurse was assessed based on information from the nationwide pension fund, which holds information for each employment held and start and end dates.
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.
Internal comparisons: age at first childbirth, number of children, place of birth, and marital status External comparisons: age
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
Beast cancer risk among nurses, compared to general population:
SIR 1.1 (95% CI 1.1-1.2)

Duration of employment in hospitals among nurses born after 1935, compared to <1 year of employment:
1-4 years: RR 1.4 (95% CI 0.9-2.1)
5-9 years: RR 1.8 (95% CI 1.1-2.6)
10-14 years: RR 1.7 (95% CI 1.1-2.5)
15-24 years: RR 1.3 (95% CI 0.9-1.9)
>/=25 years: RR 0.7 (95% CI 0.5-1.1)
Results Comments
No significant differences in associations were found when stratifying analyses by birth cohort or date of accreditation.
Author address
Department of Psychosocial Cancer Research, Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen O, Denmark. trille@cancer.dk
Reviewers Comments
Authors note that a limitation to this study is lack of control for important risk factors related to breast cancer, including smoking, alcohol use, physical activity, menopausal status, and HRT use.