THE EFFECT OF 60-HZ MAGNETIC-FIELDS ON CO-PROMOTION OF CHEMICALLY-INDUCED SKIN TUMORS ON SENCAR MICE - A DISCUSSION OF 3 STUDIES

Three independent experiments involving a total of 288 SENCAR mice wer e used to study the effects of 60-Hz magnetic fields on the growth and development of skin tumors. Given the constraints imposed by the expe rimental design, the results did not support a role for magnetic field s as a tumor co-promoter. This negative finding could also be interpre ted to mean that the SENCAR mouse skin tumor model was not sensitive e nough to detect the action of a weak co-promoter. The two-stage (initi ation/promotion) model was used to assess the genotoxic potential of m agnetic fields because it had been widely used to evaluate chemical ca rcinogens. This model, however, lacks the sensitivity to detect all bu t the most potent direct-acting carcinogens, and the tumor response to the action of low doses of promoter results in large random fluctuati ons in tumor incidence, yield and multiplicity. The need to limit tumo r incidence in the sham is a necessary condition to ensure that a magn etic field-induced effect on tumorigenesis would have a reasonable cha nce of being detected. This requirement, and the variability in tumor development between and within experiments, increases the level of unc ertainty in the system and makes a weak response to the magnetic field difficult to detect and interpret.