Environment and Breast Cancer: Science Review

Evidence From Humans
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Risks of breast and testicular cancers in young adult twins in England and Wales: evidence on prenatal and genetic aetiology
Swerdlow, A. J., De Stavola, B. L., Swanwick, M. A., Maconochie, N. E. Lancet. 1997. 350:9093, 1723-8.
Topic area
Early life exposures
Study design
Population based case-control
Funding agency
Other: Cancer Research Campaign and Medical Resear
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Number of Controls
Controls: all twin live births in England and Wales during 1939-87. Number not reported
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In cases: Twins with breast cancer diagnosed at age younger than 45 years in England and Wale during the study period In: controls: all twin live births in England and Wales during 1939-1987
Comment about participation selection
Number of controls not reported, confusing description of the results about identification of eligible and ineligible cases
Exposure Investigated
Exposures investigated
Dizygotic twinning
How exposure was measured
Questionnaire, self-administered or in person
Exposure assessment comment
Statistical estimate of zygosity when not available from questionnaire (23% of the breast cancer patients), no validation of self-report of zygosity
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, 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
Dizygotic twins compared with monozygotic twins by calculating OR with 95% CI of being dizygotic, subgroup for same-sex twins of known zygosity, risk of breast cancer in same-sex twins of breast cancer probands by cohort analysis (Standardized incidence r
Strength of associations reported
OR for dizygosity=1.0 (0.8-1.2)
SIR for same-sex twins=7.7 (4.9, 12.2)
Results Comments
The risk of breast cancer in dizygotic twins relative to monozygotic twins was not raised
Author address
Epidemiological Monitoring Unit, London School of Hygiene and Tropical Medicine, UK.
Reviewers Comments
Too much uncertainty in the numbers