Silica dust and lung cancer in the German stone, quarrying, and ceramics industries: results of a case-control study

Background-A work force based case-control study of lung cancer was perform ed in non-silicotic subjects exposed to crystalline silica to investigate t he association between silica dust and lung cancer excluding the influence of silicosis. Methods-Two hundred and forty seven patients with lung cancer and 795 contr ol subjects were enrolled, all of whom had been employed in the German ston e, quarrying, or ceramics industries. Smoking was used as a matching criter ion. Exposure to silica was quantified by measurements, if available, or ot herwise by industrial hygienists. Several indices (peak, average and cumula tive exposure) were used to analyse the relationship between the level of e xposure and risk of lung cancer as odds ratios (OR). Results-The risk of lung cancer is associated with the year of and age at f irst exposure to silica, duration of exposure, and latency. All odds ratios were adjusted for these factors. Considering the peak exposure, the OR for workers exposed to high levels (greater than or equal to 0.15 mg/m(3) resp irable silica dust which is the current occupational threshold value for Ge rmany) compared with those exposed to low levels (<0.15 mg/m(3)) was 0.85 ( 95% CI 0.58 to 1.25). For the time weighted average exposure the OR was 0.9 1 (95% CI 0.57 to 1.46). The OR for the cumulative exposure was 1.02 (95% C I 0.67 to 1.55). No increase in risk was evident with increasing exposure. Conclusions-This study shows no association between exposure to crystalline silica and lung cancer. The exclusion of subjects with silicosis may have led to dilution with respect to the level of exposure and therefore reduced the power to detect a small risk. Alternatively, the risk of getting lung cancer may be restricted to subjects with silicosis and is not directly lin ked to silica dust.