Enhanced tumor control following sequential treatments of photodynamic therapy (PDT) and localized microwave hyperthermia in vivo.

Photodynamic therapy (PDT), or photoradiation therapy (PRT), utilizing hematoporphyrin derivative (HPD) as photosensitizer and an argon-dye laser system as the light source, was used alone and in combination with localized microwave hyperthermia (2450 MHz) to treat axillary tumors of the SMT-F mammary carcinoma in mice. Thirty-minute heat treatments were applied either immediately before or immediately after a standard PDT treatment of 630 nm light at 75 mW/cm2 for 30 min (135 J/cm2) given 24 hr post-7.5 mg/kg HPD, intraperitoneally (i.p.). Tumor control as judged by lack of tumor regrowth 35 days or longer after the combined treatments was compared to that following each treatment when given alone. Little or no enhancement of tumor control was seen when sublethal temperatures of 37.5, 38.5, and 39.5 degrees C were applied for 30 min immediately following the PDT treatment. However, increasing levels of enhancement were seen when heat treatments of 40.5 and 41.5 degrees C or 44.5 degrees C, given for 30 min, were applied immediately before or after the photodynamic treatment.