[Risk apportionment to remote and recent asbestos exposures for pleural mesothelioma]

the exposure-response relationship between pleural mesothelioma and asbestos has been traditionally described by models that predicted incidence to increase indefinitely by latency. Studies with long observation showed that the increase flattens out beyond 40 years of latency. It has been, therefore, proposed to introduce an exponential decay function into the models Objectives: to show characteristics and implications as to the relevance of remote and recent exposures, by conducting a simulation exercise based on data available from the literature.

the traditional and decay models that best fit mortality from pleural cancer during the initial 40 years of observation in the Italian pooled cohort of asbestos workers were selected. The mesothelioma incidence predicted by such models as a function of age at first exposure, exposure duration, and age at risk was compared. It was also compared the proportional weight assigned to remote, intermediate, and recent exposure, by dividing the whole exposure period in three parts of equal duration.

the decay, but not the traditional, model fits well the trend observed after 40 years. According to the traditional model, remote exposures have maximum and recent exposures minimum weight: for instance, following an exposure starting at age 20 and lasting 18 years, the incidence at age 80 would be attributed to remote exposures by 47% and by 21% to the recent ones. The decay model predicts only minor differences and even of reversed weight: 34% and 31%, respectively, in this case.

remote exposures do not necessarily have overwhelming weight in determining pleural mesothelioma risk. The balance between different exposure periods depends on the time-distribution of exposure.