Environment and Breast Cancer: Science Review

Evidence From Humans
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Triazine herbicide exposure and breast cancer incidence: an ecologic study of Kentucky counties
Kettles, M. K., Browning, S. R., Prince, T. S., Horstman, S. W. Environ Health Perspect. 1997. 105:11, 1222-7.
Topic area
Environmental pollutant - Pesticide, drinking water
Study design
Other: ecologic epidemiology
Funding agency
University of Kentucky
Study Participants
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
120 Kentucky counties
Exposures investigated
Triazine herbicides. (1) Kentucky geological survey tests of 2.3% of the state's wells, oversampling in counties with heavy triazine use, multiple readings averaged across times of year; (2) tap water tests from nonrandomly selected homes using public sur
How exposure was measured
GIS/geographic location Environmental sample
Statistical Analysis
Breast cancer outcome investigated
Primary breast cancer, county breast cancer incidence
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.
% black residents, % 25 and older with B.A.; median family income, rate of first births wo women aged 30 - 44
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
Summary index: high compared with low 1991-1992 breast cancer rates OR = 1.07 (1.01-1.14); 1.20 (1.13-1.28)
Groundwater: high compared with low 1991-1992 breast cancer rates OR = 1.02 (0.96-1.08); 1993-1994 OR = 1.10 (1.04-1.17)
Surface water: high compared with low 1991-1992 breast cancer rates OR = 1.18 (1.12-1.24); 1993-1994 OR = 1.05 (1.00-1.12)
acres of corn, pesticide use: ORs < 1
Results Comments
Findings are inconsistent (not negative). Other chemicals may be correlated with those ostensibly assessed. Lack of control for urban areas. Based solely on address at diagnosis. Do high and low exposures represent an adequate range?
The incidence of breast cancer in the United States has steadily increased for the past three decades. Exposure to excess estrogen, in both natural and synthetic forms, has been implicated as a risk factor for the development of this disease. Considerable interest has been focused on organochlorines, such as the triazine herbicides, and their possible role in the initiation or promotion of human breast cancer. To explore this relationship, an ecologic study of Kentucky counties was designed. Exposure to triazines was estimated by use of water contamination data, corn crop production, and pesticide use data. A summary index of triazine herbicide exposure was developed to classify counties into low, medium, or high exposure levels. Data on county breast cancer rates were obtained from the state registry. A Poisson regression analysis was performed, controlling for age, race, age at first live birth, income, and level of education. Results revealed a statistically significant increase in breast cancer risk with medium and high levels of triazine exposure [odds ratio (OR) = 1.14,p<0.0001 and OR = 1.2, p<0.0001, respectively]. The results suggest a relationship between exposure to triazine herbicides and increased breast cancer risk, but conclusions concerning causality cannot be drawn, due to the limitations inherent in ecologic study design.
Author address
Department of Preventive Medicine and Environmental Health, University of Kentucky College of Medicine, Lexington, KY 40504-9842, USA.