Finnish researchers have published a systematic review and meta-analysis of occupational benzene exposure and the risk of leukemia that they claim is the first such study to be published.

They searched the ‘Medline’ and ‘Embase’ databases from 1950 through to July 2009 for relevant studies, and selected articles that provided information that could be used to estimate the relation between benzene exposure and cancer risk (effect size).  They identified a total of 15 studies, providing 16 effect estimates for the main analysis. Effect estimates from 9 studies were based on cumulative exposures. In these studies the risk of leukemia increased with a dose-response pattern with a summary-effect estimate of 1.64 (95% CI, 1.13-2.39) for low (<40 ppm-years), 1.90 (95% CI, 1.26-2.89) for medium (>40-99.9 ppm-years), and 2.62 (95% CI, 1.57-4.39) for high exposure category (>100 ppm-years).  In a meta-regression, the trend was statistically significant (P = 0.015).  The risk of AML also increased from low (1.94, 95% CI, 0.95-3.95), medium (2.32, 95% CI, 0.91-5.94) to high exposure category (3.20, 95% CI, 1.09-9.45), but the trend was not statistically significant. The investigators concluded their study provided consistent evidence that exposure to benzene at work increases the risk of leukemia with a dose-response pattern and that there was some evidence of an increased risk of AML and CLL, but not CML.  The study adds to the mounting evidence that cumulative occupational exposure to benzene of less than 40 ppm-years increases the risk of leukemia.  The formal citation for the study is:

Khalade, A., et al,. “Exposure to benzene at work and the risk of leukemia: a systematic review and meta-analysis,” Environ. Health 9(1):31 (June 28, 2010) [Epub ahead of print].