EFFECTS OF STEP-UP AND STEP-DOWN HEATING ON A TRANSPLANTABLE MURINE TUMOR

Abstract

The effects of step-up (42→44°sequence) and step-down (44→42°sequence) heating were studied on a transplantable mammary adenocarcinorna of C3H/He mouse. Tumor-bearing legs were immersed in a water bath and the response to hyperthermia was evaluated in terms of the delay in tumor growth. Tumor growth was delayed greatly with increase in the duration of treatment with 44°hyperthermia, whereas with 42°hyperthermia of up to 180min, tumor growth was delayed only slightly. The effects of step-up heating were similar to those of 44°hyperthermia alone and the response was enhanced by a factor of 0.9-1.1 with the 60-min treatment at 42°followed by treatment at 44°. Thermal resistance developed when the preheating time at 42°was longer than 30min. On the other hand, the tumor response was markedly enhanced by step-down heating by a factor of 1.8-2.4 with the treatment at 44°followed by 60-min treatment at 42°. Since the enhancement factor for skin damage found previously was similar to that for the tumor, therapeutic gain cannot be expected by the use of these combined heat treatments.