Environment and Breast Cancer: Science Review

Evidence From Humans
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Dioxin exposure and cancer risk: a 15-year mortality study after the "Seveso accident"
Bertazzi, P. A., Zocchetti, C., Guercilena, S., Consonni, D., Tironi, A., Landi, M. T., Pesatori, A. C. Epidemiology. 1997. 8:6, 646-52.
Topic area
Environmental pollutant - Dioxin, TCDD
Study design
Other: Cohort mortality follow up.
Funding agency
Other: Government of the Region of Lombardy, Itali
Study Participants
Number of Cases
77 breast cancer deaths
Menopausal Status
The menopausal status of women included in this study is listed here.
Pre menopausal
Post menopausal
Number in Cohort
Cohort:: 45,373 males and females in exposed zones compared with 232,747 in reference area
Cohort participation rate
< 1% loss to follow-up
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Residence in the exposed zones (A, B, R) in 1976-1991 compared with surrounding region. Identified from population registry.
Exposure Investigated
Exposures investigated
Residence in zones A, B, R in or near Seveso, Italy, after contamination by 2,3,7,8 tetrachlorodibenzodioxin (TCDD) from an industrial accident July 10, 1976. Residence determined by population registry. Exposure based on residence at the date of the ac
How exposure was measured
GIS/geographic location
Exposure assessment comment
People resident elsewhere who were in accident area at time of accident and those resident in accident area, but elsewhere at the time, were not identified. The zones represent a range of exposure, combining higher and more moderate exposures. The validity of the zones as representing a gradient of exposure has been questioned.
Statistical Analysis
Breast cancer outcome investigated
Mortality from breast cancer from 1976-1991
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.
Age, gender
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
Poisson regression
Strength of associations reported
Zone A females: 1 breast cancer death; RR 0.6 (0.0-3.1)
Zone B females: 9 breast cancer deaths; RR 0.8 (0.4-1.5)
Zone R females: 67 breast cancer deaths; RR 0.8 (0.6-1.0)
Authors state that analysis limited to those residing in the area at the time of the accident yielded similar RRs.
Results Comments
15-year follow-up is short for breast cancer. Mortality is an insensitive indicator for breast cancer. Authors state results are consistent with hypothesis that "dioxin may interfere with estrogen metabolism by favoring the metabolic pathway not associated with an increased [hormonal] cancer risk; or dioxin may compete with estrogen receptors."
Author address
EPOCA Epidemiology Research Center, University of Milan, Italy.