Abstract
BackgroundSilica and asbestos are recognized lung carcinogens. However, their role in carcinogenesis at other organs is less clear. Clearance of inhaled silica particles and asbestos fibers from the lungs may lead to translocation to sites such as the bladder where they may initiate carcinogenesis. We used data from a Canadian population-based case-control study to evaluate the associations between these workplace exposures and bladder cancer.MethodsData from a population-based case-control study were used to characterize associations between workplace exposure to silica and asbestos and bladder cancer among men. Bladder cancer cases (N = 658) and age-frequency matched controls (N = 1360) were recruited within the National Enhanced Cancer Surveillance System from eight Canadian provinces (1994–97). Exposure concentration, frequency and reliability for silica and asbestos were assigned to each job, based on lifetime occupational histories, using a combination of job-exposure profiles and expert review. Exposure was modeled as ever/never, highest attained concentration, duration (years), highest attained frequency (% worktime) and cumulative exposure. Odds ratios (OR) and their 95% confidence intervals (CI) were estimated using adjusted logistic regression.ResultsA modest (approximately 20%) increase in bladder cancer risk was found for ever having been exposed to silica, highest attained concentration and frequency of exposure but this increase was not statistically significant. Relative to unexposed, the odds of bladder cancer were 1.41 (95%CI: 1.01–1.98) times higher among men exposed to silica at work for ≥27 years. For asbestos, relative to unexposed, an increased risk of bladder cancer was observed for those first exposed ≥20 years ago (OR:2.04, 95%CI:1.25–3.34), those with a frequency of exposure of 5–30% of worktime (OR:1.45, 95%CI:1.06–1.98), and for those with < 10 years of exposure at low concentrations (OR:1.75, 95%CI:1.10–2.77) and the lower tertile of cumulative exposure (OR:1.69, 95%CI:1.07–2.65). However, no clear exposure-response relationships emerged.ConclusionsOur results indicate a slight increase in risk of bladder cancer with exposure to silica and asbestos, suggesting that the effects of these agents are broader than currently recognized. The findings from this study inform evidence-based action to enhance cancer prevention efforts, particularly for workers in industries with regular exposure.
Highlights
Silica and asbestos are recognized lung carcinogens
Most participants in these occupations were exposed at low concentrations and at medium-high frequencies
Industries with the highest proportion of workers exposed to asbestos included stationary auxiliary and utility equipment operators (50.0%), electrical, lighting and wiring installation and repair (38.3%) and product fabricating and assembling occupations and mechanics and repairers (22.2%)
Summary
Silica and asbestos are recognized lung carcinogens. their role in carcinogenesis at other organs is less clear. We used data from a Canadian populationbased case-control study to evaluate the associations between these workplace exposures and bladder cancer Both silica and asbestos are widespread in the natural environment and present in low concentrations in ambient air. Silica is a metal oxide that exists in both crystalline and amorphous forms and is a major component of sand, rock, and mineral ores It is one of the most prevalent occupational exposures worldwide with high proportions of exposed workers in occupations involving movement of the earth, such as mining, farming, quarrying, as well as construction, masonry, sandblasting, and production of glass, ceramics, and cement [1]. Inhalation is the most common route of occupational exposure to both silica and asbestos [3, 9] The latter are both recognized as human carcinogens. The impact of these exposures on the risk of cancer at other sites remains unclear
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