Livestock and poultry density and childhood cancer incidence in nine states in the USA.

Parental occupational and childhood exposures to farm animals have been positively associated with childhood brain tumors, whereas associations with childhood leukemia are equivocal. The developing immune system may be influenced by allergen, virus, or other exposures from animal sources, which may contribute to childhood cancer incidence.

We found positive associations between AML and broiler chicken densities (RRper 10AU/km2 = 1.14, 95% CI = 1.02-1.26). ALL rates increased with densities of hog operations (RRper operation/100km2 = 1.06, 95% CI = 1.02-1.11). PNS cancer rates were inversely associated with layer chicken density (RRper log of AU/km2 = 0.94, 95% CI = 0.89-0.99). No association was found between any cancer type and densities of cattle, equine, or goats