RE: The Diesel Exhaust in Miners Study (DEMS): a nested case-control study of lung cancer and diesel exhaust.

Abstract

Because our original publication (1) generated considerable interest over the past two years, we now provide additional data from our nested case-control study that are valuable in evaluating the relation between diesel exhaust exposure and lung cancer. Here we include results based on alternative exposure metrics (Table 1) and alternative approaches for adjusting for cigarette smoking as a confounder (Table 2), for comparison with results that appeared in Table 3 of Silverman et al. (1). Table 1. Odds ratios and 95% confidence intervals for average and cumulative REC lagged 15 years based on alternative exposure metrics*, † Table 2. Odds ratios and 95% confidence intervals for average and cumulative REC lagged 15 years with alternative approaches for smoking adjustment In Table 1, we estimate the lung cancer risk associated with average respirable elemental carbon (REC) intensity and cumulative REC, lagging exposure by 15 years, based on three alternative exposure metrics (2–6). The “.58” REC metrics assume that changes in REC over time are not directly proportional to changes in carbon monoxide (CO) over time, whereas the original REC metrics assumed direct proportionality (1). The “5-year mean” REC metrics use 5-year averages in CO between 1976 and the last year of the exposure assessment at each mine (1998–2001) and the ratio of horsepower over ventilation before 1976 (when CO measurements were unavailable) in the time trend models to predict historical REC levels. The “median” REC metrics were based on the median of the REC measurements instead of the mean of the REC measurements to derive the 1998–2001 reference values used in the original time trend models. Results based on these alternative exposure metrics closely reflect those originally reported in Table 3 (1), each with consistent positive trends in risk with increasing exposure. Trends tended to be highly statistically significant for cumulative REC and statistically significant or borderline significant for average REC intensity. In Table 2, we estimate the lung cancer risk associated with average REC intensity and cumulative REC, lagging 15 years, based on three approaches for smoking adjustment. We present odds ratios by increasing exposure levels adjusting for: 1) smoking status (never, former, current smoker) and duration smoked; 2) status and pack-years smoked; and 3) status and both duration and packs/day in the same model. Regardless of the approach for smoking adjustment, we observed consistent highly statistically significant trends for cumulative REC and borderline significant trends for average REC intensity. Results are strikingly consistent with the previously published odds ratios in Table 3 (1). In conclusion, these sensitivity analyses underscore the robustness of our original findings (1) and provide further evidence that diesel exhaust causes lung cancer in humans.