Environment and Breast Cancer: Science Review

Evidence From Humans
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Birth characteristics and breast cancer risk: a study among like-sexed twins
Hubinette, A., Lichtenstein, P., Ekbom, A., Cnattingius, S. Int J Cancer. 2001. 91:2, 248-51.
Topic area
Early life exposures
Study design
Retrospective cohort
Funding agency
Other: Swedish Cancer Society
Study Participants
Number of Cases
96 for within twin pair comparison, 87 for between twin pair comparison
Menopausal Status
The menopausal status of women included in this study is listed here.
Number of Controls
Controls: 96 for within twin pair comparison, 87 for between twin pair comparison
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: Cases:All female like-sexed twins born from 1886 to 1958 and included in the Twin Registry, diagnosed with invasive breast cancer in the National Cancer Registry between 1958 and 1997 and whose female co-twin was alive and had no history of breast cancer at the time when the case patient was diagnosed. Potentially eligible controls were twin pairs with registered gestational age in the birth record. Ex: uncertain birth identification or unknown gestational age
Comment about participation selection
Many women were born at home during the first half of the 20th century and had no birth record
Exposure Investigated
Exposures investigated
Birthweight, birth length, gestational age
Exposure assessment comment
Few subjects in extreme categories of gestational age
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, menopausal status, parity, alcohol consumption, family history of breast cancer (between pair comparison only)
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. Within pair comparison automatically controlled for maternal and prenatal factors. Between pair comparison conditioned on person-years at risk of developing breast cancer and birth year within 9 years. Crude OR with
Strength of associations reported
Birthweight: 1.6 (0.4-5.6); birthlength 2.0 (0.8-5.2); gestational age: 8.4 (1.3-54.4)
Results Comments
Increase risk of breast cancer in twins with long gestational age and high birth weight. The association between birth weight and breast cancer risk was not linear, although higher weight at birth seems to increase the risk
Author address
Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden. Anna.Hubinette@mep.ki.se