Histopathological study on the effects of hyperthermia on microvasculature

Recent experimental evidence suggests that hyperthermia has profound effects on tumor tissue microcirculation. Indeed, this is one of the suggested mechanisms involved in the anti-tumor effects of heat. Groups of WAG-Rij rat transplanted tumors (rbabdomyosarcoma-BA1112) were ireated with local hyperthermia (Radio-Frequency). Various temperatures (ranging from 38° to 43°C) were used. Animals were subsequently sacrificed at 1, 3, and 24 hours after beating and tumors were subjected to detailed pathological studies for evaluation of the effects of heat on microcireulation as well as on tumor cells. The results are indicative of no specific changes in microvasculature up to 40.5°C. At intermediate temperatures (42°C) vessels show marked dilatation and congestion (?stasis). At higher temperatures (44.5°C) there is massive hemorrhage and necrosis with rupture of vessel walls. The degree and intensity of this process also depends on the interval between heating and time of sacrifice of the animal. Detailed results are presented. The correlation of pathological findings and blood flow observations as well as their relevance to treatment of cancer patients are discussed.