Environment and Breast Cancer: Science Review

Evidence From Humans
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Cancer risks in twins: results from the Swedish family-cancer database
Hemminki, K., Li, X. Int J Cancer. 2002. 99:6, 873-8.
Topic area
Early life exposures
Study design
Prospective cohort
Funding agency
Other: Swedish Cancer Society, Childhood Cancer Fu
Study Participants
Number of Cases
276 same sex twins, 165 different sex twins
Menopausal Status
The menopausal status of women included in this study is listed here.
Number in Cohort
Cohort: 62,574 men and women twins
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Swedish Family-Cancer Database In : all twins aged 0-66 years born in Sweden and included in the Swedish Family-Cancer Database, cases were twin women diagnosed with breast cancer through the cancer registration
Comment about participation selection
Large cohort, results for other cancers, no data about other risk factors for breast cancer
Exposure Investigated
Exposures investigated
Same sex twin, different sex twin
How exposure was measured
Other: Family Cancer database
Exposure assessment comment
No information about 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, 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
Expected numbers of breast cancer were calculated from 5-year-age-, period- (10 year band), socioeconomic status-, and residential area-specific standard incidence rates among singletons aged 0-66 years. Standardized IR as the ratio of observed number of
Strength of associations reported
Same sex-twins: 1.01 (0.89-1.14), different sex twins: 1.04 (0.89-1.21)
Results Comments
Twinning per se is not a risk factor of breast cancer
Author address
Department of Biosciences at Novum, Karolinska Institute, Huddinge, Sweden. kari.hemminki@cnt.ki.se