This study used dimethyl benz(a)anthracene (DMBA) to promote mammary tumours in Sprague-Dawley rats. DMBA ingestion is a well-established method of promoting cancer in susceptible animals.
In each of two independent experiments, DMBA-treated animals were divided into 4 groups, with 16 per group. In each experiment there was a sham-exposed group and three groups that were exposed to GSM-900 microwaves. In the first experiment the SARs, averaged over the whole body, were 3.5, 2.2, and 1.4 W/kg in the different groups. The SARs in the exposed groups in the second experiment were 1.4, 0.7, and 0.1 W/kg.
The DMBA was administered when the rats were 55 days old, and the exposure started 10 days later. The animals were irradiated for 2 hours per day, 5 days per week, for 9 weeks.
All animals were examined every 3 days from day 20 after the DMBA treatment to detect tumour appearance, and detailed examination of the 6 pairs of mammary glands was carried out when the rats were killed 3 weeks after the end of exposure. Full histological examinations of all mammary tumours were carried out by a pathologist, blinded to the exposure status of the animals.
Results showed no difference between the groups in terms of latency, number of tumours, or tumour volumes. In the first experiment there was an increase in the rate of tumour incidence at 1.4, less at 2.2, and minimal at 3.5 W/kg. In the second experiment, however, the 1.4 W/kg group showed a decreased rate of incidence.
The authors state: