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Meta-analysis on benzene exposure and non-Hodgkin's lymphoma
  1. G M H Swaen1,
  2. S P Tsai2,
  3. C Burns1
  1. 1Department of Epidemiology, The Dow Chemical Company, Midland, Michigan, USA
  2. 2Shell Health, Shell Oil Company, Houston, Texas, USA
  1. Correspondence to Gerard M H Swaen, The Dow Chemical Company, PO Box 444, 4530 AK Terneuzen, The Netherlands; gswaen{at}dow.com

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Sir,

A recent meta-analysis on benzene exposure and non-Hodgkin's lymphoma (NHL) concluded that the reviewed epidemiologic studies provide “new evidence that benzene causes NHL.”1 The meta-analysis conducted by Steinmaus et al differed from the others in several aspects. First, it selected subgroups with the highest putative exposure to avoid dilution. Second, cohort studies were adjusted for the healthy worker effect (HWE) by considering the NHL deaths as cases and all other deaths as controls. A HWE for cancer end points is small if any compared with non-cancer end points.2 The results from a meta-analysis of 150 occupational cohort studies suggest that HWE adjustment may artificially inflate the true relative risk (RR) for cancer end points.3 Third, outdated cohort study results were used instead of more recent updates. Fourthly, Steinmaus et al did not consistently apply their own selection criteria.

We have reanalysed the meta-analysis of Steinmaus et al by precisely applying their inclusion and exclusion criteria. These include selecting the highest exposure category RR, selecting cancer incidence versus mortality data, and we used the most recent results from cohort …

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