PHOTODYNAMIC THERAPY OF FACIAL SQUAMOUS-CELL CARCINOMA IN CATS USING A NEW PHOTOSENSITIZER

Background and Objective: Photodynamic therapy has been shown to be an effective treatment modality for surface-oriented neoplasms of the sk in, respiratory, gastrointestinal, and urogenital systems. The purpose of this study was to assess the safety and efficacy of photodynamic t herapy using a new photosensitizer in the treatment of squamous cell c arcinomas of the feline facial skin. Study Design/Materials and Method s: Cats with naturally occurring squamous cell carcinomas of the facia l skin were entered into the study. Tumors were staged using a modific ation of the World Health Organization (WHO) system for classification of feline tumors of epidermal origin. Photodynamic therapy was delive red to the tumors using an argon-pumped dye laser 24 hours after the a dministration of the photosensitizer pyropheophorbide-alpha-hexyl-ethe r (HPPH-23). Following treatment, tumors were evaluated for complete r esponse rates and local control durations. Results: Fifteen tumors wer e staged T1a (< 1.5 cm diameter, noninvasive), 18 T1b (< 1.5 cm, invas ive), and 28 T2B (> 1.5 cm, invasive). Complete response rates as well as local control durations were significantly (P < 0.05) related to s tage. Complete response was achieved in 100% of T1a tumors, 56% of T1b tumors, and 18% of T2b tumors. One-year local control rates were 100% for T1a tumors and 53% for T1b tumors; overall 1-year local control r ate for all treated tumors was 62%. Clinical, hematological, and bioch emical evidence of toxicity was not seen in any cat following drug adm inistration. However, morbidity was observed following treatment of la rge, invasive tumors of the nasal plane. Conclusion: Photodynamic ther apy with the photosensitizer HPPH-23 was safe and effective in treatin g early stage squamous cell carcinomas of the feline nasal plane and f acial skin. However, toxicity was encountered following treatment of l arge neoplasms. (C) 1997 Wiley-Liss, Inc.