LEUKEMIA MORTALITY BY CELL-TYPE IN PETROLEUM WORKERS WITH POTENTIAL EXPOSURE TO BENZENE

Workers in the petroleum industry are potentially exposed to a variety of petrochemicals, including benzene or benzene-containing liquids. A lthough a large number of studies of petroleum workers have been condu cted to examine leukemia and other cancer risks, few existing studies have investigated cell-type-specific leukemias. One of the major reaso ns for the lack of cell-type-specific analysis was the small number of deaths by cell type in individual studies. In the present investigati on, all cohort studies of petroleum workers in the United States and t he United Kingdom were combined into a single database for cell-specif ic leukemia analysis. The majority of these workers were petroleum ref inery employees, but production, pipeline, and distribution workers in the petroleum industry were also included. The combined cohort consis ted of more than 208,000 petroleum workers, who contributed more than 4.6 million person-years of observation. Based on a. meta-analysis of the combined data, cell-type-specific leukemia risks were expressed in terms of standardized mortality ratios (meta-SMRs). The meta-SMR for acute myeloid leukemia was 0.96. The lack of an increase of acute myel oid leukemia was attributed to the low levels of benzene exposure in t he petroleum industry, particularly in comparison to benzene exposure levels in some previous studies of workers in other industries, who ha d been found to experience an increased risk of acute myeloid leukemia . Similarly, no increase in chronic myeloid, acute lymphocytic, or chr onic lymphocytic leukemias was found in petroleum workers (meta-SMRs o f 0.89, 1.16, and 0.84, respectively). Stratified meta-analyses restri cted to refinery studies or to studies with at least 15 years of follo wup yielded similar results. The findings of the present investigation are consistent with those from several recent case-control studies of cell-type-specific leukemia. Patterns and levels of benzene exposure in the petroleum industry are reviewed. The results of the present epi demiologic investigation are discussed in conjunction with recent adva nces in leukemogenesis from other scientific disciplines.