A cohort study of workers exposed to the chemical acrylonitrile (AN) was carried-out in the late 1980s by the National Cancer Institute (NCI) to determine if there were any excess cancer risks associated with workplace exposures to AN. The results of the study did not show any overwhelming evidence that AN exposure was related to increased cancer risk, but did yield several results worth noting. Firstly, the authors reported an overall lung cancer risk of 3.6 for ever-smokers versus never-smokers, which appeared to be much too low. Secondly, there was a slight increase in the lung cancer relative risk due to exposure in the upper quintile of cumulative AN exposure. Lastly, there was a large proportion of missing smoking information for the employees selected in the sample.
Because results of occupational cohort studies such as the NCIs are used as the basis for determining health risks associated with workplace exposures and because acrylonitrile is widely used in the manufacturing of plastics, it is very important from a public health perspective to eliminate any possible sources of confounding or bias. The goal of this reanalysis is to address the issues of missing smoking information and the low overall lung cancer relative risk in ever-smokers to determine if the slight excess in the highest AN exposure category appears to be valid. This was accomplished using imputation, a procedure that predicts a smoking status for the missings based on complete observations. The NCI analyses were then repeated with the imputed data to see if there were any differences in the overall smoking lung cancer RR or the lung cancer RR in the upper quintile of AN exposure.
The overall lung cancer RR due smoking could not be increased dramatically using the weighting schemes in this paper. Also, the lung cancer RRs in the upper quintile of AN exposure were not much lower than those in the original NCI study, so their analysis with the missing smoking information does not appear to have been biased. However, the smoking adjusted lung cancer RRs for cumulative AN exposure using the imputed data have a much flatter exposure-response trend than the NCI analysis, which, when combined with the only slightly elevated RR in the upper exposure group, could be used as evidence against an increased lung cancer risk due to high AN exposure.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-06122006-141814 |
| Date | 27 July 2006 |
| Creators | Cunningham, Michael |
| Contributors | Gary M. Marsh, Evelyn O. Talbott, Ada O. Youk |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-06122006-141814/ |
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