Benzene and haematological cancers

Haematological cancers present an example of seeming discordance between epidemiological data and animal data, which is apparently resolved by mechanistic information. Known causes of haematological cancers in humans are ionizing radiation, chemotherapeutic agents, infectious agents such as human immunodeficiency virus (HIV), and occupational exposures to chemical agents such as formaldehyde and benzene. These agents are recognized as causes of acute myeloid leukaemia (AML), and all have been implicated in the causation of other forms of haematological cancers. This chapter focuses on the issue of whether benzene can be considered to cause lymphoproliferative disorders in humans, as distinct from AML. Whereas epidemiological evidence establishes that benzene is a cause of human AML (IARC, 1987), long-term studies in experimental animals exposed to benzene generally have not indicated an increased risk of AML. In contrast, increased incidence of lymphoma has been readily evident in such studies, but the corresponding epidemiological evidence can be debated. However, recent mechanistic data, as well as information that has led to a reclassification of haematological neoplasms, are consistent with benzene being recognized as a cause of human lymphoproliferative disorders (Smith et al., 2007, Goldstein, 2010; Smith, 2010). Recent epidemiological evidence also strongly supports this notion (Bassig et al., 2015; Linet et al., 2015).