Occupational risk factors for acute leukaemia: a case-control study

A case-control study has been performed for occupational risk factors of acute leukaemia, based on 185 cases more than 30 years old and 513 matched controls. There was a significant excess of polyvalent farming and electronic engineers among professions of cases, and, in addition of metal workers when considering the professions pursued for more than 5 years. The corresponding exposures were analysed through a detailed questionnaire, and assessed by an industrial hygienist after blinding the case-control status. The odds ratios (OR) were computed after adjustment on matching variables and prior chemo- or radiotherapy treatment, and after stratification for the level and total duration of exposure. There was no excess of professional exposure to ionizing radiation among cases. A significant relationship was observed between acute leukaemia and high or medium exposure to benzene, as well as over 10 years high or medium exposure to exhaust gas. In addition a significant relationship was observed with exposure to pesticides--insecticides and/or weed killers--and to electric and magnetic fields (EMF). The relationship with pesticides was significant when considering high or medium exposure to weed killers and more than 10 years exposure to both subtypes of pesticides. The relationship with pesticides and EMF remained significant when confounding factors were taken into consideration and after adjustment on co-exposure to benzene. The cytological studies showed that acute leukaemias following exposure to benzene (high or medium) and to EMF were only of myelogenous subtypes, whereas those following exposure to pesticides were divided between lymphoblastic and myeloblastic subtypes. Cytogenetic studies failed to show increased frequency of chromosomal abnormalities, as described in acute leukaemias secondary to anti-cancer treatments. Our study adds credence to the hypothesis that pesticides and EMF are leukaemogenic agents, together with benzene.