Proceedings of Workshop on “Current Topics of Hyperthermia Oncology”

Experimental Cancer Therapy of Animal Tumor by Hyperthermia

Abstract

Effects of hyperthermic treatment on animal tumors in vivo were reviewed in order to examine clinical cancer treatment. Response of tumors to heat is not simple compared to cultured cells in vitro. Tumors are of mixed population of growing and nongrowing cells, and of aerobic and hypoxic cells. Some cells in tumors are thermosensitive due to low pH. Damages induced by hyperthermic treatment alter the tumor response.
Hyperthermic treatment at 43°C for 30 minutes reduced the surviving fraction to 19%, and the surviving fraction continued to reduce until 7% at 3 hours of the treatment; this might due to the damages of blood vessels. The fraction of hypoxic cells in tumors increased after hyperthermic treatment 24 hours of the treatment. When animals bearing tumors were bred at 4°C, thermosensitivity of tumors increased. And hyperthermic treatment as low as 40°C produced tumor control. It might be recommended that hyperthermic treatment can be repeated with 3 - 5 hour intervals, however irradiation should not be applied within 24 hours after hyperthermic treatment. And cooling tumors, if possible, might increase the tumor curability.