Implication of Blood Flow in Hyperthermic Treatment of Tumors

Tumor blood flow varies significantly depending on the type, age, and size of tumors. Furthermore, the distribution of blood perfusion in tumors is quite heterogeneous. Blood flow in tumors may or may not be greater than that in the surrounding normal tissues at normothermic conditions. When heated at 41-430C, tumor blood flow either remains unchanged or increases slightly, usually by a factor of less than 2. The newly formed tumor vessels appear to be so vulnerable to heat that the blood flow decreases at 42-43' C in most of the animal tumors studied so far. By contrast, the blood flow in normal tissues, e. g., skin and muscle, increases by a factor of 3-20 upon heating at 42-450C. Consequently, the heat dissipation by blood flow becomes greater in normal tissues than in tumors during heating, and thereby a greater temperature rise in tumors may occur, resulting in greater damage in tumor relative to normal tissues. The intrinsically acidic intratumor environment becomes further acidic upon heating and accentuates the thermal damage on the tumor cells. Blood perfusion appears to be implicated in such a heat-induced increase in the intratumor acidity.