Lung cancer mortality and airways obstruction among metal miners exposed to silica and low levels of radon daughters

Abstract

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.

Dietary vitamin A and prevalence of bronchial metaplasia in asbestos-exposed workers

“…This was true even after tobacco exposure and other covariates were controlled for. This finding is consistent with those in the literature, suggesting that a greater degree of airway obstruction (decreased FEV 1 /FVC) is associated with an increased risk of lung cancer (30)(31)(32), even after adjustment for smoking.…”

p53 and Bcl-2 expression in pneumoconiosis-related pre-cancerous lesions and lung cancers: Frequent and preferential p53 expression in pneumoconiotic bronchiolar dysplasias

“…The frequency of p53 expression in dysplasias without pneumoconiosis was very low in bronchioli, particularly in cases without lung cancer, in contrast to pneumoconiotic cases where frequent p53 expression was sustained in bronchiolar dysplasias from patients without lung cancer. These findings support epidemiological results showing a positive causal relationship between pneumoconiosis and lung cancer (Chiyotani et al, 1990;Checkoway et al, 1993;Wang et al, 1996; , 1997) and are in contrast to reports of a negative causal relationship (Meijers et al, 1990;Carta et al, 1994;Starzynski et al, 1996). We cannot specify the reasons behind our observations but speculate that certain genetic damages peculiar to pneumoconiosis might be induced frequently and preferentially in bronchiolar peripheral epithelia.…”

“…Pneumoconiosis and occupational exposure to silica have long been implicated in the pathogenesis of lung cancer (Chiyotani et al, 1990;Checkoway et al, 1993;Wang et al, 1996;Hnizdo et al, 1997), while some studies failed to find excess incidence of lung cancer with pneumoconiosis (Meijers et al, 1990;Carta et al, 1994;Starzynski et al, 1996). In addition to epidemiological studies, some in vitro and in vivo studies have demonstrated that silica per se can be carcinogenic in rats, though these data may not be applied directly to human cancers due to species-related differences in carcinogenesis (Saffioti, 1992).…”

Mortality from lung cancer among silicotic patients in Sardinia: an update study with 10 more years of follow up

“…14 From about 2000 workers investigated in our Institute in Sardinia, Italy for awarding compensation, the cohort included 724 silicotic patients who had a radiographically confirmed diagnosis between 1964 and 1970. The original chest x ray films, reviewed by two independent blinded readers, were classified according to the ILO 12 point classification scale of profusion,15 assigning a midpoint category when a disagreement between readers was present.…”