Occupational exposure and regional variation of malignant mesothelioma in Norway, 1970–79

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Abstract
This investigation is based on a study of 117 men and 24 women with malignant mesothelioma registered by the Cancer Registry of Norway, 1970–79. The age-adjusted incidence rate in men for each county varied from 1.7 to 13.3 per million per year. Eighty-two percent of the men revealed possible occupational asbestos exposure. They were evenly distributed between counties with high and low mesothelioma incidence. Only 17% of the women had possible occupational asbestos exposure. Total lung fiber concentration was analyzed with scanning electron microscopy in 65 men and 13 women. The median lung fiber concentration in men was 2.4 million per gram of dried tissue (range < 0.4–490), in women 1.0 million per gram (range < 0.4–41), and in male controls < 0.4 million per gram (range < 0.4–4.8). The median year of first exposure was 1937 (range 1909–60) for men from counties with a high incidence rate and 1945 (range 1938–59) for men from counties with a low incidence rate. The counties with a high compared to a low incidence rate of malignant mesothelioma, 1970–79, showed an apparent difference in the percentage of population employed in industry in 1946. The regional variation in the incidence of malignant mesothelioma in men is mainly attributable to the proportion of population exposed to asbestos in industry per county prior to the 1950s and the time since exposure started. Nonoccupational asbestos exposure and nonasbestos agents may be involved in some cases.