Environment and Breast Cancer: Science Review

Evidence From Humans
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Cancer incidence in the population exposed to dioxin after the "Seveso accident": twenty years of follow-up
Pesatori, A. C., Consonni, D., Rubagotti, M., Grillo, P., Bertazzi, P. A. Environ Health. 2009. 8, 39.
Topic area
Environmental pollutant - TCDD Dioxin
Study design
Prospective cohort
Funding agency
Regional Government of Lombardy (Italy) National M
Study Participants
Number of Cases
287 in Zones A, B, & R
Menopausal Status
The menopausal status of women included in this study is listed here.
No analysis based on menopausal status
Number in Cohort
Cohort: 18,649 women in Zones A, B, & R compared to 93,225 in the Referent Cohort (unexposed)
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
The Seveso cohort includes all 218,761 residents in the contaminated or reference zones at the time of the accident (July 10, 1976) and those who have migrated or were born into the region before 1986, 10 years after the accident. The cohort was followed for mortality and cancer incidence by reviewing death certificate data and linking with hospital record networks (120 hospitals in the region) through 1996.
Comment about participation selection
While the Lombardy region lacks a cancer registry, the authors were able to individually review medical records for 99.9% of cohort participants who were identified as having been admitted or discharged by a Lombardy hospital with a cancer-related diagnosis during the study period. Cohort members who emigrated outside of the region were followed with death certificates only. Emigration patterns were similar across zones, ranging from 5-7%.
Exposure Investigated
Exposures investigated
Zone of residence at the time of accident, defined by high (Zone A), medium (Zone B), low (Zone R), and no exposure (Reference Zone) based on soil TCDD contamination.
How exposure was measured
GIS/geographic location
Exposure assessment comment
The exposure zones were assigned based on residence at time of accident, an ecological surrogate of exposure. Each zone represents a range of exposure. Range of soil concentrations and median serum TCDD levels (available for a sub-population) differed across zones; levels in zone A are an order of magnitude higher than in zone B. Comparisons across zones in the sum of 20 measured congeners (Toxic Equivalency, TEQ) show differences are due to TCDD, so classification by zone may be inferred to reflect TCDD and not other congeners. However, because exposures in residences were not homogeneous within a zone, exposure misclassification is a concern.
Breast cancer outcome investigated
Primary incident breast cancer
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.
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked “Yes.” “No”, if not.
Strength of associations reported
Compared to reference zone:
Zone A (high exposure) (8 cases): aIRR 1.43 (95% CI 0.71-2.87)
Zone B (medium exposure): aIRR 0.85 (95% CI 0.59-1.22)
Zone R (low exposure): aIRR 1.00 (95% CI 0.88-1.15)

In Zone A, compared to reference zone:
0-4 years since accident: No cases reported
5-9 years since accident (1 case): aIRR 0.81 (95% CI 0.11-5.74)
10-14 years since accident (2 cases): aIRR 1.42 (95% CI: 0.35-5.68)
15+ years since accident (5 cases): aIRR 2.57 (95% CI: 1.07-6.20)
Author address
Unit of Epidemiology, Department of Preventive Medicine, Fondazione IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Via San Barnaba 8, 20122 Milano, Italy. angela.pesatori@unimi.it