[Reduction of the lung cancer risk among dairy ranchers: dose response relationship with the traditional indicators of professional exposure].

An epidemiological study of mortality was carried out in the Province of Padua in a cohort of family farmers. The subjects, identified from the SCAU files, were enrolled in the cohort if informations were available on complete registry data, date of beginning and of termination of farm work, size of farm, and number of dairy cattle. The 2,415 farmers selected were followed-up for mortality through the registry offices of their Communes of residence. The cause of death was obtained for the 541 decedents. The standardised mortality ratio (SMR) was the ratio between observed and expected mortality, calculated on the basis of the mortality rates in the regional general population. The lung cancer SMR was 0.54 (0.36-0.79; observed = 27) among the 1641 dairy farmers, and 0.78 (0.46-1.25; observed = 17) among the 774 arable farmers. Among dairy farmers, moreover, lung cancer SMRs showed a significant trend across the quartiles of length of work, number of cattle, area of farm, age at beginning farm work, and age at work termination. Dairy farmers are known to be exposed to higher airborne endotoxin concentrations, and it is reasonable to assume that this cumulative exposure further increases with years of work, number of cattle, and area of farm. Microbial endotoxin might have protected dairy farmers against lung cancer through a host factor, the Tumor Necrosis Factor, produced by alveolar macrophages.