The selective effect of heat in cancer.

Heat (42 degrees C) exerted an inhibitory effect on the oxygen uptake of the rabbit VX2 carcinoma in vitro and led to a decrease in viability and growth potential of the cells as measured by vital dye uptake and their ability to produce tumours on injection into a host. Normal host tissue cells were unaffected by elevated temperatures. After heating in vivo, tumours showed an 80-95% reduction in volume, with marked necrosis of the tumour cells. Later, macrophage invasion and replacement fibrosis were evident. There was a 50% survival rate in animals treated by local heating and a 30% survival rate in those treated by total body heating, while all the control rabbits died at 10 weeks. The selective inhibitory effect of heat on cancer cells and its application to human neoplasms are discussed.