Normal tissue and solid tumor effects of hyperthermia in animal models and clinical trials

Localized hyperthermia therapy by high-energy radio-frequency waves was evaluated in malignant and adjacent normal tissue of 30 patients with 10 types of cancer. Hyperthermia was delivered to superficial and deep visceral cancers in awake patients who had refractory disease. Histological and clinical responses were recorded serially. Toxicity tests in dogs, sheep, and pigs showed that progressive necrosis of normal and cancer tissue occurred at temperatures above 45 degrees C (113 degrees F). However, as normal tissues approached this temperature, intrinsic heat dissipation occurred (possibly due to augmented blood flow) so that temperatures below 45 degrees C could be maintained, whereas most solid tumors did not have this adaptive capacity and could be heated to 50 degrees C (122 degrees F) with virtually no injury to normal organs, s.c. tissue, or skin. To date, 69 treatments have been administered to 36 tumors in the 30 patients. Selective heating was observed in both primary and metastatic tumors located in surface tissues and internal organs. Response appeared to be related to tumor size in that differential heating was possible more often in the larger lesions. In tumors successfully heated, moderate to marked necrosis occurred. Radio-frequency hyperthermia appears to be a safe and potentially useful form of therapy for selected cancer patients. While other cancer treatments are more effective for small tumors, hyperthermia may be uniquely beneficial against larger lesions.