The International Agency for Research on Cancer (or IARC) is an arm of the World Health Organization that is charged with investigating cancer, and particularly the disease's causes. IARC reviews scientific research discussing various chemicals, and issues publications called monographs describing its review and findings.
In 1982, IARC issued Volume 29 of its monographs, which discussed a number of industrial chemicals, including benzene. Benzene is a powerful solvent that was used in industry for decades, and which is also present in other solvent products, such as toluene and xylene, as well as in gasoline and diesel fuel. At the time, IARC concluded that "[i]t is established that human exposure to commercial benzene or benzene-containing mixtures can cause damage to the haematopoetic [blood-forming] system, including pancytopenia." International Agency for Research on Cancer, World Health Organization, "Benzene," in Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans, Vol. 29: Some Industrial Chemicals and Dyestuffs, p. 127 (1982).
IARC went on to find that "[t]he relationship between benzene exposure and the development of acute myelogenous leukaemia has been established in epidemiological studies." However, IARC noted that "[r]eports linking exposure to benzene with other malignancies were considered to be inadequate for evaluation." Nevertheless, IARC determined that "[t]here is sufficient evidence that benzene is carcinogenic to man."
This year, IARC published an updated evaluation of benzene. IARC reaffirmed its previous finding that benzene is carcinogenic, observing unequivocally that "[b]enzene causes acute myeloid leukaemia/acute non-lymphocytic leukaemia." International Agency for Research on Cancer, World Health Organization, "Benzene," in Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans, Vol. 100F: Chemical Agents and Related Occupations, p. 285 (2012). In its updated monograph, however, IARC also found that "a positive association has been observed between exposure to benzene and acute lymphocytic leukaemia, multiple myeloma, and non-Hodgkin lymphoma." A link to IARC's 2012 monograph can be found here.
IARC's finding follows the German government's determination that all diseases of the blood, hematopoietic (blood-forming), and lymphatic systems can be caused by occupational benzene exposure. Beelte, S., et al., "Paradigm Change in the Assessment of Myeloid and Lymphoid Neoplasms Associated with Occupation Benzene Exposure (OD Number 1303)." Medizinische Klinik [Medical Clinic] 104(3):197-203 (2009). Notably, the German government did not limit its consideration of benzene exposure to use of benzene itself. Rather, it found that occupational exposure to products such as fuels and spray coatings could lead to benzene exposure.
Additionally, in 2010 the President's Cancer Panel, an advisory group created by federal law as part of the National Cancer Program, published a report titled Reducing Environmental Cancer Risk: What We Can Do Now. In its report, the Panel found strong evidence of a link between benzene exposure and leukemia, multiple myeloma, and non-Hodgkin's lymphoma. President's Cancer Panel, Reducing Environmental Cancer Risk: What We Can Do Now, p. A-43 (2010). A link to the President's Cancer Panel report can be found here.
Even more recently, in 2012, an international research team evaluated a group of 17 scientific studies dating back to 1993, and found "support for a possible association of occupational exposure to benzene and the risk of CML," adding chronic myelogenous leukemia to the list of diseases linked to benzene exposure. Vlaanderen, J., et al., "Occupational Benzene Exposure and the Risk of Chronic Myeloid Leukemia: A Meta-Analysis of Cohort Studies Incorporating Study Quality Dimensions." Amer. J. Indus. Med. 55:779-85 (2012).
While benzene has long been associated with diseases of the blood and blood-forming system, much of the strongest evidence has historically focused one disease---acute myelogenous leukemia. However, a mounting body of scientific evidence is tying exposure to benzene---including exposures from products of which benzene makes up only a small part---to virtually all blood diseases, including not just AML, but also multiple myeloma, non-Hodgkin's lymphoma, acute lymphocytic leukemia, and chronic myelogenous leukemia.