An extremely well-conducted meta-analysis by researchers from the Netherlands has clearly shown that occupational benzene exposure is associated with lymphoid cancers.

The researchers performed meta-analyses of occupational cohort studies for five different lymphoma categories: Hodgkin lymphoma (HL), non-Hodgkin lymphoma (NHL), multiple myeloma (MM), acute lymphocytic leukemia (ALL), and chronic lymphocytic leukemia (CLL).  They assessed three study quality dimensions to evaluate the impact of study quality variations on meta-relative risks (mRR): year-of-start of follow-up, strength of the reported AML association, and quality of benzene exposure assessment. Data synthesis mRRs for MM, ALL, and CLL increased with increasing study quality, regardless of the study quality dimension. mRRs for NHL also increased with increasing study quality, although less pronounced. The investigators concluded that their meta-analysis provides support for an association between occupational benzene exposure and risk of MM, ALL, and CLL. The evidence for an association with NHL was less clear.

This study is important, because it shows that earlier studies (conducted by industry) failed to detect increased risks of lymphoid malignancies among benzene-exposed workers, due to exposure misclassification.  The study shows that when AML is increased in the cohort (indicating true benzene exposure), the risk of lymphoid malignancies is likewise increased.  This study provides strong evidence that occupational benzene exposure causes multiple myeloma, acute lymphocytic leukemia, chronic lymphocytic leukemia, and probably non-Hodgkin’s lymphoma as well. 

Vlaanderen, J., et al., “Occupational Benzene Exposure and the Risk of Lymphoma Subtypes: a Meta-Analysis of Cohort Studies Incorporating Three Study Quality Dimensions,” Environ. Health Perspect. (Sept. 29, 2010) [Epub ahead of print]