Environment and Breast Cancer: Science Review

Evidence From Humans
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In utero exposures and breast cancer: a study of opposite-sexed twins
Kaijser, M., Lichtenstein, P., Granath, F., Erlandsson, G., Cnattingius, S., Ekbom, A. J Natl Cancer Inst. 2001. 93:1, 60-2.
Topic area
Early life exposures
Study design
Population based case-control
Funding agency
Not reported
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Number in Cohort
Controls: 90 Cohort: 13,820
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: Case subjects were female twins with male co-twins retrieved from the Swedish Twin Registry born between 1926 and 1967 who developed breast cancer between 1972 and 1995 . Control subjects were drawn from the same population, age matched, alive and without breast cancer at the time of diagnosis for the corresponding case subject. Ex: Twins with a reported gestational age of less than 33 weeks.
Comment about participation selection
No information on potential confounders like BMI or family history of breast cancer, few cases compared to the initial cohort.
Exposure Investigated
Exposures investigated
Birthweight, gestational age
How exposure was measured
Other: Birth record
Exposure assessment comment
Very few subjects in extreme categories of birthweight
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
Conditional logistic regression model conditioned on population and age and additionally adjusted for male sibling birth weight. Adjusted OR with 95% CI, birthweight: continuous analysis for 1000g of increase, gestational age: 40-44 weeks versus 33-36 wee
Strength of associations reported
Birthweight: 2.3 (1.09-4.8), gestational age: 1.5 (0.54-4.3)
Results Comments
Among female twins with male co-twins, high birthweight consitutes a risk factor for breast cancer
Author address
Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden. magnus.kaijser@mep.ki.se