Local photodynamic therapy for equine squamous cell carcinoma: Evaluation of a novel treatment method in a murine model

The objective of this study was to evaluate the effect of local photodynamic therapy (PDT) with verteporfin on tumor growth inhibition of squamous cell carcinoma (SCC) in a murine model. SCC was implanted in 85 nude mice by subcutaneous injection of A-431 SCC cells. Treatment groups (10 mice/group) received an intra-tumoral injection of verteporfin dissolved in dimethyl sulfoxide (DMSO) or 5% dextrose solution at a dose of 0.01 or 0.1 mg/cm3. Controls received only solvent, or no injectate. All groups received identical light illumination (100 J/cm2). Relative change in tumor volume (RCTV) at day 30 was compared between groups using the Wilcoxon rank sum test (P < 0.05). Local PDT with verteporfin at a dose of 0.1 mg/cm3 resulted in significantly lower RCTV at day 30 compared to controls. Choice of solvent (DMSO versus D5W) did not affect the results. Local PDT may be an effective adjunctive therapy for the treatment of periocular equine SCC.