Environment and Breast Cancer: Science Review

Evidence From Humans
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Twinship and risk of postmenopausal breast cancer
Cerhan, J. R., Kushi, L. H., Olson, J. E., Rich, S. S., Zheng, W., Folsom, A. R., Sellers, T. A. J Natl Cancer Inst. 2000. 92:3, 261-5.
Topic area
Early life exposures
Study design
Prospective cohort
Funding agency
Not reported
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Number in Cohort
Cohort: 28659 (538 twins)
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Iowa Women's Health Study In: Randomly selected women aged 55-69 years in 1986, who participated in the IWHS Ex: Women who were premenopausal, had had a mastectomy or partial breast removal, or had reported any cancer other than skin cancer at baseline in 1986. Women deceased at the time of the 1992 questionnaire or who did not respond to it, as well as women who responded to it but who had missing data on twin status
Comment about participation selection
Follow-up with 4 questionnaires during the study period
Exposure Investigated
How exposure was measured
Questionnaire, self-administered
Exposure assessment comment
Self-reported zigosity without validation
Statistical Analysis
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.
Parity, race
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
Cox proportional hazard model adjusted for educational level, family history of breast cancer, age at menarche, age at first live birth, height in meters, BMI at baseline, BMI at age 18, waist-to-hip ratio, use of hormone replacement therapy, and alcohol
Strength of associations reported
All twins: 1.72 (1.22-2.42)
Results Comments
Statistically significant, positive association between twin membership and breast cancer risk that was strongest for dizygotic female twins
Author address
Department of Health Sciences Research, Mayo Clinic, Rochester, MN 55905, USA. cerhan.james@mayo.edu