The selective inhibitory effect of hyperthermia on the metabolism and growth of malignant cells.

Hyperthermia (42° C.) exerted an inhibitory effect on the O(2) uptake of rabbit VX2 carcinoma cells in vitro, and led to a decrease in viability and growth potential of the cells, as measured by their ability to produce tumours in rabbits. Anaerobic glycolysis of the tumour cells was unaltered by hyperthermia. Respiration and anaerobic glycolysis of normal rabbit liver, kidney and red blood cells were unaffected by the elevated temperature. Local heat was applied to established VX2 tumours in vivo, with a subsequent reduction in tumour size in all cases, the most effective therapy regime being 3 one-hour applications of heat within the mean cell generation time of the tumour. Following heating there was rapid and widespread tumour cell necrosis and lysis, with subsequent replacement of the tumour architecture by connective tissue. There was a prolongation of survival time in 50% of the treated animals, which are still alive 18 months after therapy; all the control animals died within 10 weeks. The selective inhibitory effects of hyperthermia on cancer cells, and its application to human neoplasms, are discussed.