Effect of 26 week magnetic field exposures in a DMBA initiation-promotion mammary gland model in Sprague-Dawley rats

Several studies have suggested that exposure to 50 Hz magnetic fields promo te chemically induced breast cancer in rats. Groups of 100 female Sprague-D awley rats were initiated with a single 10 mg gavage dose of 7,12-dimethylb enz[a]anthracene (DMBA) at 50 days of age followed by exposure to ambient f ields (sham exposed), 50 Hz magnetic fields at either 1 or 5 Gauss (G) fiel d intensity or 60 Hz fields at 1 G for 18.5 h/day, 7 days/week for 26 weeks . A vehicle control group without DMBA was included. Rats were palpated wee kly for the presence of tumors. There was no effect of magnetic field expos ure on body weight gains or the time of appearance of mammary tumors, At th e end of 26 weeks, the animals were killed and the mammary tumors counted a nd measured. Mammary gland masses found grossly were examined histologicall y, The mammary gland carcinoma incidence was 96, 90, 95 and 85% (P < 0.05, decrease) for the DMBA controls, 1 G 50 Hz, 5 G 50 Hz and 1 G 60 Hz groups, respectively. The total numbers of carcinomas were 649, 494 (P < 0.05, dec rease), 547 and 433 (P < 0.05, decrease) for the DMBA controls, 1 G 50 Hz, 5 G 50 Hz and 1 G 60 Hz groups, respectively. The number of fibroadenomas v aried from 276 to 319, with the lowest number in the 1 G 60 Hz exposure gro up. Measurement of the tumors revealed no difference in tumor size between groups. In this breast cancer initiation-promotion study in female Sprague- Dawley rats, there was no evidence that 50 or 60 Hz magnetic fields promote d breast cancer under the conditions of this assay. This study does not sup port the hypothesis that magnetic field exposure can promote breast cancer in this rat model.