Cancer promotion in a mouse‐skin model by a 60‐Hz magnetic field: II. Tumor development and immune response

Abstract

This paper describes preliminary findings on the influence of 60-Hz (2-mT) magnetic fields on tumor promotion and co-promotion in the skins of mice. The effect of magnetic fields on natural killer (NK) cell activity in spleen and blood was also examined. Groups of 32 juvenile female mice were exposed to the magnetic field as described in part I. The dorsal skin of all animals was treated with a subthreshold dose of the carcinogen 7,12-dimethyl-benz(a)anthracene (DMBA). One week after the treatment, two groups were sham exposed (group A) or field exposed at 2 mT (group B) 6 h/day for 21 weeks, to test whether the field would act as a tumor promoter. No tumors developed in these two groups of mice. To test whether the magnetic field would modify tumor development by directly affecting tumor growth or by suppressing immune surveillance, two additional groups of mice were treated weekly with the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) and then either sham exposed (group C) or field exposed (group D). The time to appearance of tumors was shorter (but not statistically so) in the group exposed to magnetic fields and TPA. Some differences in NK cell activity and spleen size were observed between the sham- and field-exposed groups.

Assessing the Potential Carcinogenic Activity of Magnetic Fields Using Animal Models

“…The promotion experiment, using the SENCAR mouse, employed DMBA (2.56 pg) as initiator and chronic exposure (6 hr/day, 5 days/week) to 60-Hz, 2-mT continuous fields. Results were negative, confirming previous similar reports (58,59 130 ,uT, each applied in succession for 20 min followed by a 2-hr pause).…”

“…These include four pairs of lifetime or multigeneration exposure studies [(11-13) vs (16), (11-13) vs (14), (11)(12)(13) vs (15), and (14) vs (16)]; four pairs of studies using the rat mammary carcinoma promotion model [(29) vs (28), (32,38) vs (25)(26)(27), (33)(34)(35) vs (25,26,32,38), and (33,34) (the second 13-week study) vs (33,35) (the 26-week study)]; three pairs of studies using the mouse skin promotion/co-promotion model [(54) vs (58,59), (50) As shown in Table 6, aspects of the comprehensive 2-year chronic bioassay conducted by the NTP (11-13) overlap three independently conducted long-term chronic bioassays (14)(15)(16), and two of the latter three studies also have overlapping aspects (14,16 (28), (32,38) vs (25)(26)(27), and (33,34) (the second 13-week study) vs (33,35)…”

Cytokine Profile of Human Peripheral Blood Mononuclear Cells Exposed to 50 Hz EMF.

“…Lyle et a1.32~ reported the suppression of T-lymphocyte cytotoxicity following exposure to weak EMF. Further, McLean et al 33' noted a decrease in the activity of natural killer cells in mice exposed to both 7, 12-dimethylbenz(a)anthracene (DBMA), a carcinogen, and to 60 Hz EMF. Cossarizza et al 34' found that ELF pulsed EMF increased cell proliferation in lymphocytes.…”

Magnetic Fields and Cancer: Animal and Cellular Evidence: An Overview

“…A difference in the cumulated number of mice with tumors was observed, but this difference did not reach statistical significance at the end of the observation period (23 weeks). Splenomegaly (11) was observed among the TPA+ magnetic field-exposed mice, and there was a greater number of mononuclear cells in the spleens of animals with combined exposure. There was also a depressed NK cell activity.…”