Chronic lymphocytic leukaemias and non-Hodgkin's lymphomas by histological type in farming-animal breeding workers: A population case-control study based on job titles

Objectives - A population based case-control study was conducted in a highly agricultural area in the north east of Italy to evaluate the association between farming and animal breeding and the risk of developing non-Hodgkin's lymphoma (NHL) and chronic lymphocytic leukaemia (CLL). Methods - Occupational histories and other data were collected by personal interview on 164 NHLs, 23 CLLs, diagnosed in 1988-90, and on 977 controls. This paper only reports the results of the analysis relative to the coding of job titles through the modified International Labour Office (ILO) classification. Estimates of odds ratios (ORs) for occupational variables were calculated, after adjustment for sex, age, altitude of municipality, first degree familiarity, and previous Herpes zoster infection. Results - From the analysis of the most frequent occupational categories, no occupation showed a significantly high risk. When the two job titles farmers only and farmer- breeders who are also involved in animal breeding are classified within the extremely varied occupation of agriculture or animal-breeding or fishing, a high risk for NHLs and CLLs in seen in the farmer-breeders (OR 1.79, 95% CI 1.22-2.63). Analyses according to histological type show that the risks are concentrated in CLLs and in low grade NHLs. No effect or trend by period at work or duration of employment in farming and animal breeding was found. Conclusion - Subjects working in agriculture associated with animal breeding are at high risk of NHL/CLLs, particularly CLLs and low grade NHLs. This finding could be related to the use of chemicals in agriculture or to exposure to animal transmitted diseases or specific chemicals used in animal breeding.