Radiofrequency hyperthermia therapy of murine melanoma: a comparison of fractionated versus single-dose treatments.

The effects of single and fractionated doses of radiofrequency hyperthermia were investigated in the treatment of cutaneous murine melanoma. S91 murine melanoma cells were implanted into preformed intradermal blister cavities on the backs of DBA/2J mice. Evaluation of treatment response was undertaken after single and fractionated doses of hyperthermia. A single 60-second treatment at 46 degrees C did not result in any complete regressions, while 3 weekly 46 degrees C treatments produced a 40% incidence of tumor regression. Higher temperature therapy was associated with improved cure rates. A single treatment for 60 seconds at 50 degrees C resulted in a 25% complete response rate while 3 weekly 50 degrees C treatments resulted in the eradication of 92% of the treated tumors. In those tumors that responded only partially to hyperthermia, fractionated low- (46 degrees C) and (50 degrees C) high-dose regimens resulted in significantly smaller melanomas than single-treatment schedules at the same temperatures. It is concluded that fractionated hyperthermia is an effective modality in the control of intracutaneous murine melanoma. If other cutaneous malignancies are also sensitive to heat, this may provide a useful nonsurgical means of treating skin cancer.

Radiofrequency hyperthermia and topical retinoic acid therapy in murine melanoma.

Malignant cells are known to be sensitive to increased temperature. The effects of hyperthermia (HT) on intradermally implanted S91 melanoma cells in syngeneic mice were investigated with a hand-held radiofrequency generator. The possible additive effects of topical retinoic acid (RA) in this system also were studied. Five millimeter diameter melanomas were treated with either HT alone, RA alone, or a combination of HT and RA and were then evaluated after 43 days and 59 days. Eighteen of 20 tumors treated with HT alone and all 20 melanomas treated with HT/RA were eradicated. RA alone caused complete regression in 11 of 19 treated tumors. It is concluded that radiofrequency HT is an effective treatment in intradermal murine melanoma and that the addition of RA does not significantly alter the outcome because of the extreme effectiveness of HT alone.