Photodynamic Therapy of Feline Cutaneous Squamous Cell Carcinoma Using a Newly Developed Liposomal Photosensitizer: Preliminary Results Concerning Drug Safety and Efficacy

Abstract

Background: Squamous cell carcinomas are common skin tumors in cats. We investigated photodynamic therapy (PDT) using a new liposomal photosensitizer as a minimally invasive, effective treatment that can be easily performed while achieving good cosmetic results. Aim: The goal of this study was to assess and describe possible toxicities using a liposomal formulation of the photosensitizer meta‐(Tetrahydroxyphenyl)Chlorin (m‐THPC) and investigate if favorable pharmacokinetics translate into favorable tumor response and control. Animals: Eighteen client‐owned cats with 20 spontaneous cutaneous squamous cell carcinomas were included in the study. Methods: PDT was performed using a new, liposomal formulation of the photosensitizer. Toxicity, tumor response, and tumor control were evaluated retrospectively. Results: No general adverse effects were observed in cats treated with the new liposomal formulation. Mild local toxicity such as erythema and edema were seen in 15% of the patients. All cats responded to therapy, with a complete response rate of 100%. The overall 1‐year control rate was 75%. The tumor recurrence rate was 20% with a median time to recurrence of 172.25 (±87.1) days. Conclusions and Clinical Importance: A new liposomal photosensitizer was successfully used for squamous cell carcinoma in cats and was well tolerated. There were no systemic adverse effects observed with the liposomal formulation. The favorable pharmacokinetics of the liposomal drug resulted in a favorable tumor response.