膀胱がん死亡の地理疫学 -市郡別分布を中心に-

Abstract

Geographic variation in bladder cancer mortality was evaluated on a basis of smaller area (city and county) than prefecture in Japan. Age and sex specific numbers of bladder cancer deaths for 1, 123 areas were obtained from unpublished national mortality statistics for 1969~71. Corresponding populations were provided by 1970 census. Annual specific mortality for the age of 40 years and over was computed. Among 1, 123 areas, 71 areas(6.3%)in males and 63 areas(5.6%) in females were identified as the areas with significantly higher mortality than the national average. These areas dispersed throughout Japan in both sexes. The areas with high mortality, defined as the areas where the ratio of the mortality over the national average was 1.4• and over, were also distributed dispersively, but tended to cluster in rural districts. Of interest, such areas were not observed in cluster along the Pacific coast, with many highly industrialized areas and large cities. Significance of this geographic pattern was tested by a simmulation model based on Monte Carlo method, revealing statistically insignificant clusters in Japan. The areas with high mortality were geographically indifferent to a sociomedical variable such as geological, meteorogical, demographic or socioeconomic chatacteristics. To determine the industrial makeup of the areas with high bladder cancer mortality, the percentage of male workers in 46 separate industries were compared with corresponding percentages for the areas with low mortality. In this comparison, the areas were restricted to the cities with male lung cancer mortality not different from the national average. This stipulation was aimed to select the cities where bladder cancer risk was more likely related to industrial exposure than to cigarette smoking. The cities with high bladder cancer mortality had a significantly high percentage of workers in agriculture, fishery, mining, and manufacturing of textile products, or stone, clay, glass and pottery products, and a significantly low percentage of workers in the industries manufacturing electric machinery, equipment and supplies, or precision machines, and also in department stores and broadcasting services. This particular finding was presumed to be the industrial reflection of the fact that the areas with high bladder Cancer mortality were mainly observed in rural districts in Japan. Under the above stipulation of male lung cancer mortality, the percentages of male workers were similarly compared between the cities with the greater male-to-female ratio of bladder cancer mortality than 1.5 and those with the ratio of almost unity (greater than 0.7 and less than 1.3). The industries, probably related to the excess risk for males in bladder cancer, were found to be those manufacturing textile products, pulp, paper and allied products, rubber products, leather, fur and their products, iron, steel and non-ferrous metal products, fabricated metal products, electric machinery, equipment and supplies, or precision machines, and also publishing, printing and related industries. The present analysis is accordingly presumed to confirm the occupational carcinogenesis in bladder cancer. Other environmental and socioeconomic factors relevant to rural districts are also believed to be of etiological importance in Japan.