Environmental Factors in Breast Cancer: Enhancing an Ecological Epidemiology Study Through the Use of a Geographic Information System. S. R. Swedis, R. A. Rudel, Y. T. Joyce, and J. G. Brody, Silent Spring Institute, 29 Crafts Street, Newton, MA 02158 and Applied Geographics, Inc., 100 Franklin Street, Boston, MA 02110
Between 1982-1992, nearly all Cape Cod towns had higher than expected rates of breast cancer, compared with statewide rates. Previous studies of cancer incidence on the Cape have not indicated that the elevated rates can be explained by screening practices, length of residence on the Cape, or traditional risk factors for breast cancer. Because of the regional pattern of the observed elevated rates, the role of environmental factors in breast cancer is a focus of current research. This paper reports on the tools and methods used to enhance standard ecologic epidemiology methods to examine the association between potential exposure to endocrine disruptors and selected other environmental factors and the incidence of breast cancer on Cape Cod. Ecologic epidemiology provides an efficient, cost-effective method for studying environmental health using data available only on the group level and that may have been collected previously for other purposes. The method is limited by its focus on group level, rather than individual level data, and by the resulting likelihood of exposure misclassification. Our study uses a Geographic Information System (GIS) to enhance the capabilities of the ecological epidemiology in several ways. It permits us to (1) map the residential location of all cases diagnosed over 11 years down to the individual parcel level; (2) closely define areas of potential exposure to environmental agents by linking detailed environmental data of diverse types such as historical and current environmental quality data, changes in land use, and hydrogeological data; and (3) identify non-contiguous areas that may be similar in potential exposures so that population data may be joined to increase the statistical power of epidemiological analyses. The result is a complex, integrated ecologic epidemiology study that is conducted at a level of detail not achievable using manual methods.
Work supported by the Massachusetts Department of Public Health under Contract # SC-DPH-7900-62-14H11.