| Triazine Herbicide Exposure and Breast Cancer Incidence: An Ecologic Study of Kentucky Counties Michele A. Kettles, Steven R. Browning, Timothy Scott Prince, and Sanford W. Horstman Department of Preventive Medicine and Environmental Health, University of Kentucky College of Medicine, Lexington, KY 40504-9842 USA Abstract
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. Key words : breast cancer, ecologic study, organochlorines, pesticides, triazine herbicides, xenoestrogens. Environ Health Perspect 105:1222-1227 (1997) .
Address correspondence to M.A. Kettles, Department of Preventive Medicine and Environmental Health, University of Kentucky College of Medicine, 1141 Red Mile Road, Lexington, KY 40504-9842 USA. We thank Robert Millikan for his helpful comments and Carla Koford for her assistance with data files and data entry. This research was supported by a grant from Behavioral and Research Aspects of Safety and Health (BRASH) Working Group, University of Kentucky. Received 11 February 1997 ; accepted 11 July 1997.
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