Exposure to benzene at work and the risk of leukemia: a systematic review and meta-analysis

Background A substantial number of epidemiologic studies have provided estimates of the relation between exposure to benzene at work and the risk of leukemia, but the results have been heterogeneous. To bridge this gap in knowledge, we synthesized the existing epidemiologic evidence on the relation between occupational exposure to benzene and the risk of leukemia, including all types combined and the four main subgroups acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), and chronic myeloid leukemia (CML). Methods A systematic literature review was carried out using two databases 'Medline' and 'Embase' from 1950 through to July 2009. We selected articles which provided information that can be used to estimate the relation between benzene exposure and cancer risk (effect size). Results In total 15 studies were identified in the search, providing 16 effect estimates for the main analysis. The summary effect size for any leukemia from the fixed-effects model was 1.40 (95% CI, 1.23-1.57), but the study-specific estimates were strongly heterogeneous (I2 = 56.5%, Q stat = 34.47, p = 0.003). The random-effects model yielded a summary- effect size estimate of 1.72 (95% CI, 1.37-2.17). 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). Use of cumulative exposure eliminated heterogeneity. 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. Conclusions Our study provides consistent evidence that exposure to benzene at work increases the risk of leukemia with a dose-response pattern. There was some evidence of an increased risk of AML and CLL. The meta-analysis indicated a lack of association between benzene exposure and the risk of CML

Occupational exposure to Benzene and risk of Cancer

This thesis assessed the risk of cancer in relation to exposure from benzene at work. The thesis is in three major sections. The first section consisted of a systematic review and meta-analysis to assess the risk of leukemia from occupational exposure to benzene. The systematic review confirmed leukemia to be important in relation to benzene exposure; 15 selected studies yielded 16 effect estimates with an overall statistically significant effect size (relative risk) of 1.40 (95% CI, 1.23-1.57). A dose response analysis was performed and provided evidence for a strong positive trend between leukemia risks and estimated exposure to benzene. The risk of all leukemia combined increased with a dose-response pattern with a summary effect size (ES) of 1.64 (95% CI 1.13-2.39) for low (100 ppm-years). The risk of AML also increased from low (ES 1.94, 95% CI 0.95-3.95), medium (ES 2.32, 95% CI 0.91-5.94) to high exposure category (ES 3.20, 95% CI 1.09-9.45), but the trend was not statistically significant. The second section used the same method to assess other cancer risks by conducting a systematic review and further meta-analysis. The most common other cancer sites for which a possible occupational involvement from benzene has been suggested were lung, bladder, melanoma, stomach and kidney cancer. Consequently, a systematic review and meta-analysis was performed on each of these cancer sites. The results obtained did not show any clear evidence of risk for lung cancer (ES 0.99, 95% CI 0.96-1.03), bladder cancer (ES 1.00, 95% CI 0.96-1.03), or stomach cancer (ES 0.96, 95% CI 0.90-1.03). However increased risks were shown for melanoma (ES 1.25, 95% CI 1.09-1.44) and kidney cancer (ES 1.14, 95% CI 1.04-1.25). The systematic review and meta-analysis for melanoma was based on 7 available studies reporting 8 cohorts. It was not possible to conclude that benzene exposure is a cause of melanoma as many other chemicals were also used in the factories. There was no significant heterogeneity in the study-specific findings for melanoma (P=0.26). The systematic review and meta-analysis for kidney cancer was based on 22 available studies reporting 24 cohorts. There was also no significant heterogeneity in the study-specific findings for kidney cancer (P=0.41). Therefore, further research is needed to establish a strong link between exposure to benzene and risk of kidney cancer. The final section of the thesis examined the risk of leukemia, lung cancer and all cause mortality in workers exposed to benzene in a large cohort of workers employed at 233 factories during 1966/67 in England & Wales. The results however provided no clear evidence of a dose response effect for leukemia risks in relation to estimated cumulative exposure from benzene. The major limitations of the study related to the recording of limited work histories and the collection of incomplete or limited exposure assessments. The method used in recording the levels of exposure were not clear as different factories were measured by individual personnel at differing times over the years, and at differing areas within factory to factory. It was not possible, therefore, to gain a comprehensive and consistent exposure assessment throughout the factories. To obtain an accurate and viable outcome there needs to be a sound measurement of exposure technique implemented such as taking personal samples using a personal sampler for each individual and indicating specific areas where low, medium and high exposures are evident alongside adequate ventilation. Job exposure matrix also needs to be considered alongside socio-economic classification and ethnicity as this may show some effect on how different minorities may be better or worse adapted to certain chemical exposures

Involving interpreters in research studies

It is important to include non English speakers in health services research to ensure not only the generalisability of findings but also to address health inequalities and promote social justice. One approach is to use interpreters but there is little guidance for working with an interpreter in interviews. Involving an interpreter presents challenges in the planning and conduct of research interviews which can be minimised by an awareness of various theoretical and practical implications and of potential pitfalls. Drawing both on our experiences of involving interpreters in research and on the literature, we raise some issues that researchers need to consider. </jats:p