Environment and Breast Cancer: Science Review

Evidence From Humans
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Effect of twinship on incidence of cancer of the testis, breast, and other sites (Sweden)
Braun, M. M., Ahlbom, A., Floderus, B., Brinton, L. A., Hoover, R. N. Cancer Causes Control. 1995. 6:6, 519-24.
Topic area
Early life exposures
Study design
Prospective cohort
Funding agency
Other: John D. and Catherine T. MacArthur Foundati
Study Participants
Number of Cases
254 monozygotic twins and 486 dizygotic twins
Menopausal Status
The menopausal status of women included in this study is listed here.
Number of Controls
9486 monozygotic twins and 16055 dizygotic twins
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: Swedish Twin Registry, twin individuals of known zygosity born during the years 1886 through 1925 who were still alive in 1961 and twin individuals born during the years 1926 through 1958 who were still alive in 1971
Comment about participation selection
Lack of information about other breast cancer risk factors
Exposure Investigated
Exposures investigated
Zygosity of twins (monozygote, dizygote)
Exposure assessment comment
Determination of zygosity not fully determined, validation study of reported zygosity not explained
Statistical Analysis
Breast cancer outcome investigated
Primary incident breast cancer
Ethnic groups with separate analysis
If this study provided a separate analysis by ethnic or racial group, the groups are listed here.
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.
BMI, race, parity, menopausal status, alcohol consumption, family history of breast cancer
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked “Yes.” “No”, if not.
Description of major analysis
O/E ratio (observed cases compared with expected incidence of breast cancer estimated with the use of age and calendar specific cancer incidence rate for the Swedish General Population) with 95% CI, separate analysis for monozygotes and dizigotes, stratif
Strength of associations reported
All monozygotes: 1.0 (0.9-1.2), all dizygotes: 1.1 (1.0-1.2),
Results Comments
Zygosity groups did not show notable elevation in O/E ratios for breast cancer, except among dizygotic twin women aged 20-29 years 6.7, CI = 2.9-13.1
Author address
Environmental Epidemiology Branch, US National Cancer Institute, Bethesda, MD, USA.