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RESEARCH PRODUCT

Effect of Localized Hyperthermia on Tumor Blood Flow and Oxygenation

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Hyperthermia has been shown to have a lethal effect in tumor cell cultures, particularly at temperatures above 42°C.1 Moreover, it has been demonstrated that hyperthermia retards the growth rate of certain types of malignant tumors and can be effective in completely eradicating some tumors without any major damage to normal tissue.2,3,4 The differential response of solid tumors in vivo to heat treatment in comparison to normal tissue probably results from several factors. Among these the in vivo micro-environment seems to play a decisive role. In general, the interstitial milieu of solid tumors is characterized by tissue hypoxia and anoxia5,6 and by severe tissue acidosis.7 These unfavorable micro-environmental conditions are mainly caused by a deterioration of nutritive blood flow and by inadequate removal of metabolic waste products. Since both pH and O2 tensions are known to be critical determinants of the thermal sensitivity of tumor cells,8,9 the effectiveness of hyperthermia in solid tumors may vary according to the efficiency of tumor blood supply. On the other hand, a possible impact of elevated tissue temperatures on tumor blood flow and on cellular metabolism can induce changes in tissue pH and/or tissue pO2 values thus modifying the direct cell-killing effect of hyperthermia.