Cell biology effects of ultrasound and microwave hyperthermia

Abstract

Hyperthermia, or elevated temperature in the 41 °C to 50 °C range, in cancer treatment has been the subject of intense renewed interest over the past decade. This interest has come about primarily for three reasons: (1) conventional therapies such as ionizing radiation and chemotherapy have failed in several disease categories, (2) historical anecdotal reports of tumor responses after episodes of fever, and (3) the development of instrumentation systems for the controlled and reproducible administration of tumor temperature elevation such as ultrasound and microwaves. Until recently it was thought that cancer cells possessed an intrinsic sensitivity to these elevated temperatures, however, application of the ever more sophisticated techniques of modern cellular and molecular biology have demonstrated that solid tumor physiological factors, such as a lowered pH and nutrient deprivation appear to be the responsible factors rather than the transformation to malignancy. Other studies have demonstrated that hyperthermia can also result in dramatic enhancement of the more conventional therapies in addition to the heat‐induced cytotoxicity. This latter enhancement comes about by the alteration of membrane permeabilities and the inhibition of subcellular repair mechanisms and in some cases, both effects. These observations have led to several studies to develop possible advantages of the various methods of tumor temperature elevation, however no specific effects of either ultrasound or microwaves have been documented other than those attributed to the elevation of tissue temperatures. [Supported in part by CA‐17891 and CM‐17524 from the NCI.]