Environment and Breast Cancer: Science Review

Evidence From Humans
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Risk factors for breast cancer at young ages in twins: an international population-based study
Swerdlow, A. J., De Stavola, B. L., Floderus, B., Holm, N. V., Kaprio, J., Verkasalo, P. K., Mack, T. Journal of the National Cancer Institute. 2002. 94:16, 1238-46.
Topic area
Body size - Physical Activity
Study design
Pooled population based case-control (retrospective)
Funding agency
NCI ACS Other: Danish Cancer Society, Cancer Resea
Study Participants
Number of Cases
400 (50 Denmark) (217 England and Wales) (27 Finland) (106 Sweden)
Menopausal Status
The menopausal status of women included in this study is listed here.
Pre menopausal
Number of Controls
Control: twins sisters of cases
Country where study was conducted
UK, Sweden, Finland and Denmark
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: women diagnosed with incident breast cancer before the age of 50 (cases); twin sisters of cases (controls); resident of Denmark, England, Wales, Finland or Sweden during recruitment period of the respective study; completed in-person interview or mailed questionnaire Ex: either twin had died before age 6 or either twin had emigrated (Denmark)
Comment about participation selection
Strengths: self-reported cases were verified histologically, by cancer registries or by medical records; zygosity was known for 93.5% of twin pairs; population based analysis of breast cancer risk in twins by body size; analyzed breast cancer risk in twins by physical activity; twins studies based on self-reported anthropometric data have less recall bias than studies on individual subjects; one of the few studies to analyze the relationship between waist to hip ratio and risk of premenopausal breast cancer; one of the few studies to analyze the relationship between premenopausal breast cancer and adult exercise among women with a family history of the disease Limitations: did not specify how anthropometric data were obtained; did not report participation rate; small number of cases in each of the case-control studies; retrospective study; possibility that cases and controls were overmatched, which could decrease the apparent magnitude of the effects of an exposure; datasets in each of the four studies differed in years and inclusion/exclusion criteria
Exposure Investigated
Exposures investigated
Height at 20, weight at 20, body shape at 20 (waist, hip and breasts) and physical activity
How exposure was measured
Questionnaire, in person Questionnaire, self-administered
Exposure assessment comment
Not all anthropometric data were obtained by trained staff
Early life exposures considered
Height, weight, body shape and physical activity
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.
Adequately controlled, Confounders: parity, weight and height at different ages
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
Effect modifiers: menopausal status (pre only)
Results Comments
Childhood growth before puberty may affect the risk of premenopausal breast cancer. The risk of premenopausal breast cancer was not statistically significantly associated with the relative size of waist, hips or breasts of twins at age 20 years. Women who were taller than their co-twin at age 10 years but not at age 20 years had a lower risk of premenopausal breast cancer than did women who were the same height as their co-twins at both ages (not significant). OR for premenopausal breast cancer in relation to adult exercise was more greatly reduced in women with familial breast cancer than in those with nonfamilial breast cancer.
Author address
Section of Epidemiology, Institute of Cancer Research, Sutton, UK. a.swerdlow@icr.ac.uk