Exposure to benzene and non-Hodgkin lymphoma, an epidemiologic overview and an ongoing case-control study in Shanghai

The interest in the relationship between benzene exposure and non-Hodgkin lymphoma (NHL) appears to have been generated from a 1979 publication, which reported an increased risk of NHL among persons potentially exposed to benzene and/or coal tar fractions. More recently (1997), an increased risk of NHL was reported among 74,828 workers exposed to benzene and other chemicals in a variety of industries in China. On the contrary, no increased risk of NHL was reported in a cohort of 1,165 workers at two rubber hydrochloride plants in Ohio (US), who were exposed to extremely high levels of benzene and were found to have an increased risk of acute myeloid leukemia. In another large cohort of some 7,676 US workers exposed to benzene, no increased risk of NHL was reported. Similarly, no increased risk of NHL was reported in a combined cohort of 308,199 petroleum workers in the US, the UK, Canada, Australia, Italy and Finland, who were exposed to benzene or benzene-containing petroleum products. The lack of an association between benzene exposure and NHL in cohort studies is supported by case-control studies from the US, Canada, Italy and the UK. To further investigate the relationship between benzene exposure and NHL, we are conducting a hospital-based case-control study in Shanghai, China. Cases are newly diagnosed NHL patients at 29 hospitals in Shanghai. For each case, two matched controls are selected among patients without any lymphatic or hematopoietic diseases at the same hospital. Demographic, employment, medical and lifestyle information is obtained through questionnaires (primary and secondary). Sources for benzene exposure information include a database of 50,000+ benzene measurements maintained by the Shanghai Municipal Institute of Public Health Supervision (IPHS), Shanghai District IPHS, walk-through surveys at factories, additional measurements at factories and reports in Chinese medical journals. Patient enrollment started in 2003 and it is estimated that the study will have 400-450 NHL cases by December 2006. Some of the occupations or industries reported among enrolled study subjects (cases and controls) with potential exposure to benzene include shoe workers, painters, mechanics or machinists, and printers. Some of the unique features of the study are discussed.