Effect of 13 week magnetic field exposures on DMBA-initiated mammary glandcarcinomas in female Sprague-Dawley rats

Several studies suggest that exposure to 50 Hz magnetic fields may promote chemically induced breast cancer in rats. Groups of 100 female Sprague-Dawl ey rats were initiated with four weekly 5 mg gavage doses of 7,12-dimethylb enz[a]anthracene (DMBA) starting at 50 days of age. After the first weekly DMBA administration, exposure to ambient fields (sham exposed), 50 Hz magne tic fields at either 1 or 5 G field intensity or 60 Hz fields at 1 G for 18 .5 h/day, 7 days/week was initiated. Exposure continued for 13 weeks. A veh icle control group without DMBA was included. In a second study, using lowe r doses of DMBA, groups of 100 female Sprague-Dawley rats were initiated wi th four weekly doses of 2 mg of DMBA starting at 50 days of age followed, a fter the first weekly DMBA administration, by exposure to ambient fields (s ham exposed) or 50 Hz magnetic fields at either 1 or 5 G field intensity fo r 18.5 h/day, 7 days/week for 13 weeks. Rats were weighed and palpated meek ly for the presence of tumors. There was no effect of magnetic field exposu re on body weight gains or on the time of appearance of mammary tumors in e ither study. At the end of 13 weeks, the animals were killed and the mammar y tumors counted and measured, Mammary gland masses found grossly were exam ined histologically. In the first 13 week study, the mammary gland carcinom a incidences were 92, 86, 96 and 96% for the DMBA controls, 1 G, 50 Hz, 5 G , 50 Hz and 1 G, 60 Hz groups, respectively. The total numbers of carcinoma s were 691, 528 (P < 0.05, decrease), 561 and 692 for the DMBA controls, 1 G, 50 Hz, 5 G, 50 Hz and 1 G, 60 Hz groups, respectively. In study 2, the m ammary gland carcinoma incidences mere 43, 48 and 38% for the DMBA controls , 1 G, 50 Hz and 5 G, 50 Hz groups, respectively. The total numbers of carc inomas were 102, 90 and 79 for the DMBA controls, 1 G, 50 Hz and 5 G, 50 Hz groups, respectively. There was no effect of magnetic field exposure on tu mor size either by in-life palpation or by measurement at necropsy in eithe r study. There was no evidence that 50 or 60 Hz magnetic fields promoted br east cancer in these studies in female rats. These studies do not support t he hypothesis that magnetic field exposure promotes breast cancer in this D MBA rat model.