Environment and Breast Cancer: Science Review

Evidence From Humans
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A population-based study of cancer risk in twins: relationships to birth order and sexes of the twin pair
Swerdlow, A. J., De Stavola, B., Maconochie, N., Siskind, V. Int J Cancer. 1996. 67:4, 472-8.
Topic area
Early life exposures
Study design
Population based case-control
Funding agency
Other: Medical Research Council and Cancer Researc
Study Participants
Number of Cases
79 second born/76 first born
Menopausal Status
The menopausal status of women included in this study is listed here.
Number of Controls
Controls: not reported
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: Female twins diagnosed with breast cancer, residents of England and Wales and born since 29 September 1939
Comment about participation selection
Description of methodology very complex and incomplete
Exposure Investigated
Exposures investigated
Second born twin
How exposure was measured
Other: National Register
Exposure assessment comment
Validity of registers to really report birth order of twins
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
OR with 95% CI of second-born versus first born twins using control data based on twin live births in England and Wales, by sex, for the years of birth of the cancer cases, 1939-1984, Stratified analysis by the sex of co-twin, study period: 1971-1984
Strength of associations reported
OR second born: 1.06 (0.77-1.48)
Results Comments
No association of twin birth order with the risk of breast cancer
Author address
Epidemiological Monitoring Unit, London School of Hygiene and Tropical Medicine, UK.