Evidence for microwave carcinogenesis in vitro.

We investigated the carcinogenic activity of 2.45 GHz microwave radiation (MW) combined with benzo[a]pyrene (BP) or X-rays, using an in vitro assay for malignant transformation in C3H/10T1/2 mouse-embryo fibroblasts. Additional experiments were performed to assess the effect of a non-cytotoxic and non-transforming concentration of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) on transformation induction in cells treated with MW and X-rays. Experiments were performed at low incident power density, corresponding to an energy absorption rate of 4.4 W/kg. Cells were treated at 37.2+/-0.1 degree C. MW reduced the plating efficiency of 50%, while TPA increased it by 40%. MW had no effect on transformation induced by BP or X-rays in the absence of tumor promoter. TPA treatment of cells previously irradiated with MW and X-rays yielded a statistically significant 3.5- or 1.6-fold increase in transformation when compared with the transformation frequency of cells previously irradiated with X-rays alone at 1.5 and 4.5 Gy, respectively. Our results suggest that low-level 2.45 GHz MW radiation can induce latent transformation damage which can then be revealed by the action of tumor promoters.