| Research Abstract |
In the south east of Okayama Prefecture, Japan, there have been reports on high prevalence of silicosis among refractory brick production workers, and excess risk of lung cancer among the residents. Therefore, a population based case-control study was conducted on the relationship between silica, silicosis, and lung cancer.
Cases and controls were restricted to male subjects and obtained from death certificates from 1986 to 1993 in the area. Four kinds of deceased control groups were selected ; the series of deaths from liver cancer, colon cancer, and cancers of the other organs, which assumed not to be related to silica exposure. Age and smoking habits were adjusted by stratified analysis using the Mantel-Haenszel odds ratio estimates. Unconditional logistic regression analysis was also conducted for controlling potential confounding factors ; such as age and smoking habits.
The age-, smoking-adjusted odds ratios were 1.59 (0.87-3.03) for liver cancer control, 1.94 (0.94-4.43) for colon
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cancer control, and 2.13 (1.19-3.85) for the other cancer control on silica exposure, and 2.45 (1.22-5.34), 2.94 (1.30-8.90), and 2.69 (1.43-5.37) on silicosis, respectively. Histologic or cytologic types of lung cancer cases were obtained from 64.1% (118/184). On histologic types of lung cancer, small cell carcinoma may related to silica exposure after comparing with unexposed lung cancer cases and the data from the general Japanese population. On the findings of chest X-ray, elevated lung cancer mortality compared with other cancers than lung was demonstrated among the patients without large opacities.
Silica exposure increased the lung cancer mortality in the area. The results support the causal relationship between silica exposure and lung cancer, designated by IARC in 1997. From now, the relationship between silica exposure and esophagus cancer, gastric cancer, liver cancer. and hematopoietic malignancy which has been reported the association to silica exposure should be investigated and examined. Less
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