The average period of asbestos exposure for these 28 patients was 20 years. Malignant pleural mesothelioma developed more than 40 years after the first exposure to asbestos. Many asbestos particles and fibers were detected in the lungs and tumors of these patients. Most of the asbestos fibers detected were crocidolites or amosites. Considering that the amount of asbestos used in Japanese has been higher than in any other country, the incidence of malignant pleural mesothelioma may be expected to increase in this country.
Countermeasures are now advisable.
Besides asbestos exposure, the factors that determine susceptibility to malignant mesothelioma are unknown. The mortality of 3,246 males who had been employed 1 or more years during 1940-1980 at 20 crushed stone operations was evaluated for possible association between employment and death from lung cancer, pneumoconiosis, and other respiratory diseases. Four deaths were attributed to pneumoconiosis. Based on available work histories, at least two of these deaths were probably due to dust exposures in the crushed stone industry. Although not definitive, results of this study are consistent with the hypothesis that exposure to respirable silica dust is a risk factor for lung cancer.