[Thermotolerance of tumors MA737 and LA795 of mice]

The effects of splitted heating of tumor, alone or in combination with local radiation, were studied on mouse mammary cancer MA737 in JB 2 mice and lung cancer LA795 in 739 mice. Hyperthermia was done by immersing the tumor-bearing foot into a water bath at 44 +/- 0.2 degrees C. When combined with radiation, 8 Mev beta irradiation from a linear accelerator was given. The response was assessed by tumor growth retardation calculated according to a special computer program. A priming dose of 5 to 6-minute exposure to 44 degrees C was followed, after various time intervals (1, 4, 5, 24 hr), by a longer exposure. Thermotolerance was induced in these two animal tumor models. Tolerance to heat, however, did not affect the combined effect of hyperthermia and radiation. Electron microscopic examination of the treated tumors confirmed the synergistic killing effect of the combined treatment.