Lack of promotion effects of 50 Hz magnetic fields on 7,12-dimethylbenz(a)anthracene-induced malignant lymphoma/lymphatic leukemia in mice

New‐born CD‐1 mice were initiated with a single subcutaneous injection of 60 µg 7,12‐dimethylbenz(a)anthracene (DMBA) within 24 h after birth. After weaning, the mice were randomly divided into five groups of 100, 50 males and 50 females each. One group served as a cage control. The other four groups of mice were exposed to either 0 (sham‐exposed), 7, 70, or 350 µT(rms) circularly polarized 50 Hz magnetic fields (MFs) for 22 h/day, 7 days/week for 30 weeks. Animals were observed daily and the development of malignant lymphoma/lymphatic leukemia was examined histopathologically. The experiment was conducted twice. There was no observed sexual difference in the cumulative proportions of mice with malignant lymphoma/lymphatic leukemia and a 3‐way analysis of deviance using the Cox regression model revealed no interactions between experiment, sex, or group. The cumulative proportions of mice with malignant lymphoma/lymphatic leukemia in the MF‐exposed groups were not significantly higher than those in the sham‐exposed group of each sex in individual experiments and in males and females combined in each experiment, and in all the animals from the two experiments combined. These data provide no evidence to support the hypothesis that power frequency MFs is a significant risk factor for hematopoietic neoplasia. Bioelectromagnetics 29:29–38, 2008. © 2007 Wiley‐Liss, Inc.