Exposure to 60 Hz magnetic fields and risk of lymphoma in PIM transgenic and TSG-p53 (p53 knockout) mice

The results of a number of epidemiology studies suggest that exposure topower frequency (50 and 60 Hz) magnetic fields may be a risk factor forhematopoietic neoplasia. To generate experimental data to test thishypothesis, the influence of magnetic field exposure on lymphoma inductionwas determined in two strains of mice that are genetically predisposed tothe disease. PIM mice, which carry the pim-1 oncogene, are highly sensitiveto lymphoma induction by N-ethyl-N-nitrosourea (ENU); ENU-treated PIM micewere studied as a 'high incidence' lymphoma model. TSG-p53 (p53 knockout)mice, in which the p53 tumor suppressor gene has been deleted from the germline, develop lymphoma as an age- related change; hemizygous TSG-p53 micewere studied as a 'low incidence' lymphoma model. Beginning 1 day after asingle i.p. injection of 25 mg ENU/kg body wt, groups of 30 PIM mice/sexwere exposed for 18.5 h/day to pure, linearly polarized, transient-free 60Hz magnetic fields at field strengths of 0 (sham control), 0.02, 2.0 or10.0 Gauss (G). An additional group of 30 PIM mice/sex was exposedintermittently (1 h on, 1 h off) to 10.0 G fields. Groups of 30 TSG-p53mice/sex were exposed continuously to magnetic field strengths of 0 (shamcontrol) or 10.0 G; TSG-p53 mice received no ENU. Studies were terminatedafter 23 weeks of magnetic field exposure. Lymphoma incidence in male PIMmice exposed continuously to 10.0 G magnetic fields was significantlyreduced from that seen in sex-matched sham controls; survival, lymphomaincidence and lymphoma latency in other groups of PIM mice did not differfrom sham controls. Survival and lymphoma incidence in all groups ofTSG-p53 mice was 7% or less, regardless of magnetic field exposure regimen.These data do not support the hypothesis that exposure to magnetic fieldsis a significant risk factor for lymphoid neoplasia in mice with a geneticpredisposition to the disease.