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Sorahan and colleagues1 recently published the results of a cohort mortality and morbidity study of workers purportedly exposed to benzene in the UK. Despite inherent problems with their data analyses, the authors nevertheless concluded that “the study does not support claims that exposure to benzene affects risks for lymphohaematopoietic malignancies other than ANLL”. In my opinion, the discrepancies and flawed analyses preclude this study from being used to make any health determination for workers exposed to benzene.
Lack of information on cancer deaths among cohort members
The authors admit to evidence of “under-ascertainment,” or non-identification, of cancer registrations. This is an understatement. Indeed, with the exception of cancer of the lip (2 observed versus 0.2 expected), the highest risk of cancer achieving statistical significance was “cancers of uncertain origin” (SMR = 140, based on 68 cancer deaths, p < 0.001). Their morbidity analysis also suffers from “under-ascertainment” for specific types of cancer experienced by these workers as the authors state that an estimated 60 cancer registrations remained untraced.
Closer scrutiny of their data also reveals an even greater problem with “under-ascertainment” of cancer deaths during the 1968–74 follow up period—the period of death for those cohort members who likely experienced the highest benzene exposure levels. For the 1968–74 follow up period, I estimate that 51% (46 of 91) of the cancer deaths had no information provided on their specific type of cancer. My analysis is as follows: the data in table 2 of the Sorahan et al report1 indicate that 761 cancer deaths occurred during the entire follow up period of 1968–2002. In the …
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