Background: Numerous studies have been carried out to evaluate the association between lung cancer and occupational asbestos exposure. However, the effects of timing of exposure have not been analyzed thoroughly.
Methods: Two German case-control studies with data on occupational asbestos exposure histories have been pooled. Duration of work in potentially asbestos exposed jobs and two derived weighted exposure measures are analyzed together with time since last exposure. A spline function is used to model the effect of time since exposure.
Results: The odds ratios (OR) and corresponding 95% confidence intervals were 1.8 (1.2, 2.7) and 2.4 (1.7, 3.4) for subjects having worked for 3 to 7 years and 8 or more years, respectively, in a job with potential asbestos exposure compared to never-exposed. Based on an evaluation of time since last exposure, the OR decreased significantly to about one-half after more than 20 years since exposure ceased. Using a spline function, applied to workers' complete exposure histories, the effect of an increment of exposure is greatest 10-15 years after that exposure was received.
Conclusions: In contrast to previous indications, the risk of lung cancer increases soon after asbestos exposure, with its maximum effect from 10 to 15 years after the exposure was received.