Photodynamic therapy and hyperthermia as an adjuvant modality in preventing tumor recurrence

Background and Objective: The objective of this study was to determine the relative efficacy in preventing tumor recurrence by photodynamic therapy (PDT), and by ablative CO₂ laser surgery followed by PDT, compared to ablative surgery alone (negative control) or ablative surgery followed by a course of hyperthermia (positive control). Study Design/Materials and Methods: The cheek pouches of 36 hamsters were treated with 0.5% 9,10 dimethyl-1,2-benzanthracene in acetone three times a week. After 12 weeks all animals showed tumors of their cheek pouches and were divided into four groups. In groups number I, II, and III, all visible tumors were removed by aid of a CO₂ laser. Animals of group I did not receive any further treatment. After tumor resection, the cheek pouches in group II were treated with hyperthermia by aid of a Nd:YAG laser and a temperature of 43°C for 30 minutes. In group III after resection of the tumors, the cheek pouches were treated with PDT (75mW/cm² 175J/cm²-3mg/kg Photofrin i.p./24h). In group IV, the tumors were not excised, instead they were only treated with PDT (as above). All animals were observed for 50 days for any signs of tumor recurrence. Results: In group I (CO₂) all tumors (100%) recurred within 50 days. In group II (CO₂ + hyperthermia) 61%, in group III (CO₂ + PDT) 27.7%, and in group IV (PDT) 50% of all tumors recurred. The first signs of recurrence could be seen in group I, followed by groups II and IV. Group III was the last one presenting tumor recurrence. Conclusions: The combination of CO₂ surgery and PDT produced significantly better results than CO₂ surgery or PDT alone, and better than the combination of CO₂ surgery and hyperthermia.