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We read with interest the article by Sorahan et al, “Cancer risks in a historical UK cohort of benzene exposed workers”.1 We note that the authors showed an increased SMR and SRR for lung cancer among this group. They comment that “there was evidence of increased mortality for lung and lip cancers and for ANLL, and increased morbidity for lung and pleural cancers. There is no reason to suspect that benzene is responsible for the increased lung and pleural cancer risks in this study.” The authors then go on to point out that it is likely that some members of the cohort were exposed to other lung carcinogens. However, we feel that if this was a likely explanation for the observed excess, then the SMR for lung cancer would probably have been heterogeneously distributed among the industries studied, the risk being elevated only in those industries with known exposures to lung carcinogens. This does not seem to have been the case. Further, confounding by cigarette smoking seems unlikely because the SMR for some other tobacco related causes are not significantly elevated (for example, non-malignant diseases of the respiratory system).
There have been two papers based on a Chinese cohort of benzene exposed workers,2,3 which are relevant to this issue. The first showed an RR for lung cancer of 2.31 among exposed non-smokers, and while 95% confidence intervals were not reported, the authors did state this was statistically significant.2 The second reported a relative risk for lung cancer of 1.4 (95% CI 1.0 to 2.0) among benzene exposed males.3 Therefore, we think it is important to recognise that while the excess described in this paper may be due to exposure to other carcinogens, it is also possible that we are seeing accumulating evidence of an association between benzene exposure and lung cancer.
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