[Biological bases of cancer treatment by hyperthermia]

There is little difference in heat sensitivity in vitro between normal and cancer cells. However, rather selective tumor destruction is induced by in vivo heating without affecting normal tissues. This selective effect may be attributed to heat-induced vascular damage causing reduction in the supply of oxygen and nutrients, and a decrease in the pH of tumors. These cellular environmental changes greatly enhance hyperthermic cytotoxicity. Besides this, antitumor immunity of host animals is also involved in the selective effect of hyperthermia. Hyperthermia potentiated the actions of various antitumor agents including nitrosoureas, cisplatin and bleomycin. The effect of heating on adriamycin cytotoxicity depends on the cell lines used; in some cell lines the cytotoxic effect is enhanced by 42-43 degrees hyperthermia, but in some other cells it is enhanced only at 40-41 degrees and drug-resistance is induced at 43 degrees. Benzaldehyde is nontoxic at 37 degrees but has greatly enhanced cytotoxicity by combination with hyperthermia.