title: Acceleration of mammary tumorigenesis by exposure of 7,12-dimethylbenz[a]anthracene-treated female rats in a 50-Hz, 100-microT magnetic field: replication study.
abstract: In view of the methodological problems of epidemiological studies on associations between residential and occupational exposures to 50/60-Hz magnetic fields (MF) and increased incidence of cancers, laboratory studies are necessary to determine if 50/60-Hz MF can affect cancer development or growth. Recently, it was reported that alternating (50-Hz) MF of low flux density (100 microT) increase tumor growth and progression in a model of breast cancer in female rats in which mammary tumors were induced by the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA). The objective of the present study was to determine if a replicate experiment carried out in the same laboratory under the same experimental conditions yields a significant increase in tumor development and growth of similar magnitude. For the MF experiment, a group of 99 female Sprague-Dawley rats was exposed to a homogeneous horizontally polarized MF for 24 h/d (minus time for weighing, tumor palpation, cage cleaning, cage rotation), 7 d/wk; another group of 99 rats was sham exposed. DMBA was administered intragastrically at a dose of 5 mg/rat at the first day of exposure and at weekly intervals thereafter up to a total dose of 20 mg/rat. Duration of MF or sham exposure was 91 d. In both MF-exposed and sham-exposed rats, the first tumors could be recorded 6 wk after the initial DMBA application. At 9 wk after DMBA application, the group of MF-exposed rats exhibited significantly more animals with tumors than the sham-exposed group. This significant difference in the rate of tumor development was observed throughout the subsequent period of exposure. After autopsy, the incidence of macroscopically visible mammary tumors was 62% in controls, but 83% in MF-exposed rats, with the 35% difference between groups being statistically significant. Data substantiate that long-term exposure of DMBA-treated female Sprague-Dawley rats in an alternating MF of low flux density promotes the development and growth of mammary tumors, thus indicating that MF exposure exerts tumor-promoting and/or copromoting effects. Furthermore, the data show that the effects of MF exposure in the DMBA breast cancer model are reproducible if the same experiment is repeated in the same laboratory.
authors.affiliation: Department of Pharmacology, Toxicology, and Pharmacology, School of Veterinary Medicine, Hannover, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Mevissen
authors.forename: M
authors.initials: M
authors.lastname: Häussler
authors.forename: A
authors.initials: A
authors.lastname: Lerchl
authors.forename: W
authors.initials: W
authors.lastname: Löscher
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene; D000818:Animals; D002273:Carcinogens; D004195:Disease Models, Animal; D004574:Electromagnetic Fields / Q000009:adverse effects*; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced / Q000209:etiology* / Q000473:pathology; D008550:Melatonin / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012107:Research Design
chemical_list: D002273:Carcinogens; D015127:9,10-Dimethyl-1,2-benzanthracene; D008550:Melatonin