Environment and Breast Cancer: Science Review

Evidence From Humans
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Breast cancer risk in monozygotic and dizygotic female twins: a 20-year population-based cohort study in Finland from 1976 to 1995
Verkasalo, P. K., Kaprio, J., Pukkala, E., Koskenvuo, M. Cancer Epidemiol Biomarkers Prev. 1999. 8:3O, 271-4.
Topic area
Early life exposures
Study design
Prospective cohort
Funding agency
Other: Imperial Cancer Research Fund Cancer Epidem
Study Participants
Number of Cases
66 monozygotic twins+179 dizygotic twins
Menopausal Status
The menopausal status of women included in this study is listed here.
Premenopausal and postmenopausal combined and separate
Number in Cohort
Cohort: 4308 monozygotic twins+8868 dizygotic twins=13176 female twins
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Finnish Twin Cohort Study In: all of the female-female twin pairs with known zygosity in which both co-twins were living in Finland on December 31, 1975.
Comment about participation selection
The validity of zygosity information collected from questionnaire has been proved through comparing with results from polymorphic blood markers.
Exposure Investigated
Exposures investigated
Monozygotic twinning, dizygotic twinning
How exposure was measured
Questionnaire, mailed
Exposure assessment comment
Self-reported zygosity information
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
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
The expected numbers of breast cancer were calculated using age- and calendar-period-specific cancer incidence in Finland. The SIRs (95% CI) for monozygotic (MZ), dizygotic (DZ) and all twins were computed by dividing the observed number of cases by the e
Strength of associations reported
MZ: SIR=0.76 (0.76, 0.97)
DZ: SIR=0.98 (0.84, 1.1)
All: SIR=0.91 (0.80, 1.0)
SIRmz/SIRdz=0.78 (0.58, 1.0)
Author address
Department of Public Health, University of Helsinki, Finland. p.verkasalo@icrf.icnet.uk