Does local tumour heating im mice influence metastatic spread?

Experimental studies are reported on the effect of local tumour hyperthermia, combined with radiation, on the incidence of distant metastases. Two types of study were performed: a retrospective analysis of data obtained incidentally from regrowth delay experiments, and prospective studies designed specifically to investigate the effect of heat on the spread of disease. In the first case, tumours were treated with a range of palliative doses of X rays given either alone or in combination with heat (42.8 degrees C/h). Only one tumour out of 5 showed a significantly increased incidence of metastases, and then only when heated immediately before radiation. The prospective studies were designed so that primary tumours were locally controlled. Neither heat applied immediately before nor after irradiation resulted in a significant change in incidence of metastases. However, whole body heating did produce a marginally significant increase. Fractionated hyperthermia (4 heat doses plus curative radiation) did not result in any significant change in frequency of metastasis. These data suggest that local heating combined with radiation does not result in an increased risk of metastatic spread.