Starting from a cross-sectional survey in 1973, the mortality of two cohorts of Sardinian metal miners was followed through December 31, 1988. In mine A, the quartz concentration in respirable dust ranged between 0.2% and 2.0% and the exposure to radon daughters averaged 0.13 working level (WL), with the highest estimated cumulative exposure around 80-120 WLM. In mine B, the silica content was much higher (6.5-29%), but exposure to radon daughters was significantly lower than in mine A. More than 98% of the overall work force in 1973 (1,741 miners) entered the cohort, providing 25,842.5 person-years. Smoking, occupational history, chest radiographs, and lung function tests were available for the cohort members at admission. Mortality for all causes was slightly lower than expected. A significant excess for nonmalignant chronic respiratory diseases was noticed in both mines. Twenty-four subjects died of lung cancer, 17 from mine A (SMR: 128; 95% confidence interval [CI]: 75-205) and 7 from mine B (SMR: 85; 95% CI: 34-175). The SMR for lung cancer was highest among the underground workers from mine A (SMR: 148; 95% CI: 74-265), with a significant upward trend by duration of employment in underground jobs. Mine B underground miners showed lung cancer SMRs close to 100 without a significant trend by duration of employment. Among underground miners with spirometric airways obstruction in 1973, those from mine A showed the highest risk (SMR: 316; 95% CI: 116-687). The relationship did not change after adjusting for age and smoking. Based on the present findings, crystalline silica per se does not appear to affect lung cancer mortality. A slight association between lung cancer mortality and exposure to radon daughters, though within relatively low levels, may be considered for underground miners from mine A. Impaired pulmonary function may be an independent predictor of lung cancer and an important risk factor enhancing the residence time of inhaled carcinogens, i.e., alpha particles or PAHs, by impairing their bronchial and alveolar clearance.
The mortality of 4740 male workers of two lead and zinc mines was followed up from 1960 for subjects employed 26 years, was, however, found among underground workers in mine A who on the average experienced an exposure to radon daughters 10-fold higher than those of mine B. By contrast, despite their higher exposure to silica, mine B underground workers experienced a lower than expected lung cancer mortality. A ninefold increase in risk of peritoneal and retroperitoneal cancer combined was also found among underground workers ofmine A (SMR 917; 95% CI 250-2347; based on four deaths). A causal association with workplace exposures is unlikely, however, as the SMR showed an inverse trend by duration of employment. These findings are consistent with low level exposure to radon daughters as a risk factor for lung cancer among metal miners. Exposure to silica at the levels estimated for the mine B underground environment did not increase the risk of lung cancer. (Occup Environ Med 1994;51:674-682)
A case-control study was conducted to test the hypothesis whether the genetic condition of glucose-6-phosphate dehydrogenase (G6PD) deficiency is associated with a reduced risk of cancer. One hundred and eighty seven male cancer patients admitted to hospitals in Cagliari (Sardinia, Italy), between November 1984 and March 1986, were compared with 186 male patients with other diseases, except hemolytic anemia, admitted to the same hospitals in the same period. In contrast to previous reports, our study found no reduction of cancer risk in G6PD-deficient subjects. The study had sufficient statistical power to detect a 0.5-fold decrease in the risk of cancer. The recent suggestion from other studies that tumoral cells of G6PD-deficient subjects can produce their own G6PD, seems to be consistent with this negative finding. Among those subjects presenting some level of erythrocyte G6PD activity, the average enzyme activity was significantly higher in cancer patients than in controls. This finding is consistent with previous experimental studies suggesting a positive correlation between cell proliferation and G6PD activity.
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