Lack of effect of a 60 Hz magnetic field on biomarkers of tumor promotion in the skin of SENCAR mice

It has been proposed that extremely low frequency magnetic fields may enhance tumorigenesis through a co-promotional mechanism. This hypothesis has been further tested using the two-stage model of mouse skin carcinogenesis, i.e. 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced promotion of skin carcinogenesis in mice initiated by a single subcarcinogenic dose of 7,12-dimethylbenz[a]anthracene. Experimentation utilized three different doses of TPA within its dose-response range (0.85, 1.70 or 3.40 nmol) and examined the following early biomarkers of tumor promotion after 1, 2 and 5 weeks of promotion: increases in epidermal thickness and the labeling index of epidermal cells, induction of epidermal ornithine decarboxylase activity and down-regulation of epidermal protein kinase C activity. Mice exposed to a 60 Hz magnetic field having a flux density of 2 mT for 6 h/day for 5 days/week were compared with mice exposed to an ambient magnetic field. Within the sensitivity limits of the biomarker methodology and the exposure parameters employed, no consistent, statistically significant effects indicative of promotion or co-promotion by the magnetic field were demonstrated.