Environment and Breast Cancer: Science Review

Evidence From Humans
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An epidemiological study of cancer in adult twins born in Norway 1905-1945
Iversen, T., Tretli, S., Kringlen, E. Br J Cancer. 2001. 84:11, 1463-5.
Topic area
Early life exposures
Study design
Cohort study
Funding agency
Not reported
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Number in Cohort
Cohort: 23,334 male and female twins
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: Twins born in Norway during 1905-1945 who were both alive in 1960
Comment about participation selection
Long follow up, however only based on registers, analysis for other cancer sites
Exposure Investigated
How exposure was measured
Other: National Register
Exposure assessment comment
Did not find some women who change their name on marriage (number not reported)
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.
Age, 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
SIR (observed number of new cases of breast cancer in the cohort during the follow-up with expected number of the total population of the country) with 95% CI, follow-up 1960-1996
Results Comments
Weak and non significant inverse association of breast cancer and female twins
Author address
The Department of Oncology, Ullevaal Hospital, Oslo, Norway.