Interaction of hyperthermia and photoradiation therapy

Local microwave hyperthermia (2450 MHz) was applied to axillary implants of the SMT-F mammary carcinoma in mice in combination with photoradiation therapy (PRT) in an attempt to determine if the two modalities interact. When 40.5 degrees C was applied for 30 min immediately prior to or immediately following PRT (630-nm light, 30 min, at 75 mW/cm2, 20-24 hr post 7.5 mg/kg hematoporphyrin derivative), enhancement of tumor response over that of PRT alone was seen as judged by lack of tumor regrowth (35 days or longer after treatment). A temperature of 41.5 degrees C applied for 30 min immediately following the 30-min PRT treatment produced a result slightly greater than that seen at 40.5 degrees C. When a temperature of 44.5 degrees C for 30 min was applied immediately following PRT, a substantial enhancement of tumor control at 35 days post-treatment was found (53% versus 19 and 4%, respectively, for hyperthermia and PRT alone). These results suggest that tumor response to PRT is enhanced by both a sublethal hyperthermic treatment (40.5 degrees C, 41.5 degrees C) and a moderately lethal heat treatment (44.5 degrees C) given for a short duration, when applied immediately before or after photoradiation.