[Experimental study on the anti-tumor effect of microwaves]

C3H/He mice bearing a mammary carcinoma, MM2, were treated by systemic hyperthermia with microwave irradiation (2450 MHz). An output of 30 watts of microwaves for 5 min at a distance of 20 cm from the animal raised and maintained the rectal temperature of mice to higher than 42 degrees C for 2.2 min and higher than 40 degrees C for 10.2 min. The mice were inoculated i. p. with MM2 tumor cells (2 X 10(6) cells/mouse), and then they were exposed to hyperthermia every day; 10 watts for 2, 4, or 6 min, or 20 watts for 2, 4, 6 min. The control mice receiving no irradiation and the mice treated with irradiation of 10 watts for 2 min or 20 watts for 2 min died within 21-23 days. Whereas, 40 percent of the mice treated with microwave irradiation of 10 watts for 4 or 6 min, or 20 watts for 4 or 6 min survived longer than 30 days. The 6 mice, which survived longer than 120 days, were challenged by reinoculation with MM2 tumor cells (2 X 10(6)cells/mouse). All the mice but one survived longer than 30 days with no accumulation of ascites. These experimental data suggest that the systemic hyperthermia with microwave irradiation (24 50 MHz) might suppress the tumor growth in vivo.