Hyperthermia in the treatment of cancer.

There is now considerable evidence that heat can be used to destroy tumours. The metabolism of many types of cancer cell is selectively damaged at temperatures of 42-43 degrees C, and deficient tumour blood-flow at raised temperature represents a further exploitable Achilles heel. A striking feature of tumour heating is that metastases may regress with cure of the host; this has occurred with recurrent melanoma and sarcomas of the limbs. Heat acts synergistically with X-rays and some cytotoxic drugs to increase the therapeutic ratio for local tumour control. Guidelines for tumour heating are now being formulated against a strong experimental background in animal systems. The association of a wide variety of disciplines from oncology to electronics has already resulted in techniques for selectively treating human tumours at 50 degrees C and in internal heat applicators for insertion via natural passages. It is predicted that heat will achieve a place, most likely as an adjuvant, in cancer therapy. Work on animals and in vitro is of limited value in helping to define this place. The complexity of the tumour/host response to heat and the deficiencies in our knowledge of the biophysics of heating militate against early routine application of hyperthermia in the clinic.