Spatial distribution of cancer incidence by anatomic site in Quebec

Knowledge of the spatial distribution of diseases provides useful information in etiologic research and in implementation of preventive activities in community health. Spatial autocorrelation analysis is one of the various methods that enables to determine spatial clustering of diseases. This method has not been applied to lung, stomach and colon cancer in Québec. These cancers are frequent and are associated with environmental factors. The objectives of the study are to determine spatial distribution of incidence rates of these cancer sites by sex and to help generate etiologic hypotheses. Community health departments (CHDs) of residence are considered as risk markers since their population and environment may be related to the selected cancer sites. Data were obtained from Québec Cancer Registry. Rates were standardized by the direct method. Autocorrelation analysis was done through BW coefficient and Moran's coefficient I for correlograms. Results of standardized rates were compared to those of non standardized rates. Rates yielded the same results for the BW coefficient. Conversely, results were quite different for the correlograms. This implies that results from standardized rates should be kept since the age structure of CHD populations are different. Important variation in the level of spatial autocorrelation was found among the six sex-specific cancer sites. For male lung cancer and male stomach cancer first-order neighbouring CHDs showed similar incidence rates according to a geographic gradient. Female lung cancer exhibited spatial autocorrelation. Absence of spatial autocorrelation for colon cancer suggests that CHD is not the appropriate scale for study of this cancer and allows use of conventional epidemiologic methods. These results are discussed in relation to current etiologic hypotheses.